Method for driving semiconductor device

ABSTRACT

The resolution of a low-resolution image is made high and a stereoscopic image is displayed. Resolution is made high by super-resolution processing. In this case, the super-resolution processing is performed after edge enhancement processing is performed. Accordingly, a stereoscopic image with high resolution and high quality can be displayed. Alternatively, after image analysis processing is performed, edge enhancement processing and super-resolution processing are concurrently performed. Accordingly, processing time can be shortened.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to display devices, liquid crystal displaydevices, semiconductor devices, production methods thereof, or methodsfor using the display devices, the liquid crystal display devices, orthe semiconductor devices. In particular, the present invention relatesto driving methods of display devices, liquid crystal display devices,semiconductor devices, or the like, or signal processing methodsthereof.

2. Description of the Related Art

In recent years, flat panel displays typified by liquid crystal displayshave been widely used. In addition, flat panels have been furtherimproved in many respects. One of specifications of flat panels isresolution (or the number of pixels). Resolution has also beendrastically improved.

Therefore, a super-resolution processing technology, which is atechnology for converting low-resolution images into high-resolutionimages, has been studied (see References 1 to 3).

REFERENCE

Reference 1: Japanese Published Patent Application No. 2008-160565

Reference 2: Japanese Published Patent Application No. 2008-085411

Reference 3: Japanese Published Patent Application No. 2008-252701

SUMMARY OF THE INVENTION

In liquid crystal displays, a variety of methods for improving imagequality have been studied. Therefore, in flat panel displays typified byliquid crystal displays, in the case where processing for improvingimage quality is performed, a variety of problems may be caused. Forexample, any of the following problems may be caused; the decrease inimage quality, impossibility of display of correct images, the increasein power consumption, the increase in noise, necessity of extracomponents, the increase in cost, the increase in the size of devices,the increase in the frames of display devices, the decrease inprocessing speed, the decrease in display speed, and the decrease inframe frequency.

From the above, it is an object of one embodiment of the presentinvention to provide a device having higher image quality, a drivingmethod thereof, or a manufacturing method thereof. Alternatively, it isan object of one embodiment of the present invention to provide a devicewhich displays a correct image, a driving method thereof, or amanufacturing method thereof. Alternatively, it is an object of oneembodiment of the present invention to provide a device with low powerconsumption, a driving method thereof, or a manufacturing methodthereof. Alternatively, it is an object of one embodiment of the presentinvention to provide a device with little noise, a driving methodthereof, or a manufacturing method thereof. Alternatively, it is anobject of one embodiment of the present invention to provide a devicehaving fewer components, a driving method thereof, or a manufacturingmethod thereof. Alternatively, it is an object of one embodiment of thepresent invention to provide a device manufactured at low cost, adriving method thereof, or a manufacturing method thereof.Alternatively, it is an object of one embodiment of the presentinvention to provide a smaller device, a driving method thereof, or amanufacturing method thereof. Alternatively, it is an object of oneembodiment of the present invention to provide a device with a narrowframe, a driving method thereof, or a manufacturing method thereof.Alternatively, it is an object of one embodiment of the presentinvention to provide a high-speed processing device, a driving methodthereof, or a manufacturing method thereof. Alternatively, it is anobject of one embodiment of the present invention to provide a devicewhich performs display at high speed, a driving method thereof, or amanufacturing method thereof. Alternatively, it is an object of oneembodiment of the present invention to provide a device whose framefrequency is not low, a driving method thereof, or a manufacturingmethod thereof. Alternatively, it is an object of one embodiment of thepresent invention to provide a device with fewer afterimages, a drivingmethod thereof, or a manufacturing method thereof. Alternatively, it isan object of one embodiment of the present invention to provide ahigh-contrast device, a driving method thereof, or a manufacturingmethod thereof. Note that the description of these objects does notimpede the existence of other objects. Note that in one embodiment ofthe present invention, there is no need to achieve all the objects.

After image processing such as edge enhancement is performed, alow-resolution image is converted into a high-resolution image with asuper-resolution processing technology. Then, data processing for localdimming (local luminance control) using a backlight and/or dataprocessing for overdrive can be performed, for example.

Alternatively, after image processing such as edge enhancement andinterpolation of frame data for displaying an image at higher framefrequency, a low-resolution image is converted into a high-resolutionimage with a super-resolution processing technology. Then, dataprocessing for local dimming using a backlight and/or data processingfor overdrive can be performed, for example.

Alternatively, image processing such as edge enhancement andsuper-resolution processing (conversion of a low-resolution image into ahigh-resolution image) are performed concurrently. Then, data processingfor local dimming using a backlight and/or data processing for overdrivecan be performed, for example.

Therefore, a method for driving a semiconductor device, which includes afirst step of performing edge enhancement processing and a second stepof performing super-resolution processing, is provided. The second stepis performed after the first step.

Alternatively, a method for driving a semiconductor device, whichincludes a first step of analyzing an image, a second step of performingedge enhancement processing, and a third step of performingsuper-resolution processing, is provided. The second step or the thirdstep is performed after the first step. A period during which the secondstep and the third step are concurrently performed is provided.

Alternatively, a method for driving a semiconductor device, whichincludes a first step of performing edge enhancement processing, asecond step of performing frame interpolation processing, a third stepof performing first super-resolution processing, and a fourth step ofperforming second super-resolution processing, is provided. The thirdstep or the fourth step is performed after the first step or the secondstep.

Alternatively, a method for driving a semiconductor device, whichincludes a first step of performing edge enhancement processing, asecond step of performing frame interpolation processing, a third stepof performing super-resolution processing, and a fourth step ofperforming local dimming processing, is provided. The third step isperformed after the first step or the second step. The fourth step isperformed after the third step.

Alternatively, a method for driving a semiconductor device, whichincludes a first step of performing edge enhancement processing, asecond step of performing frame interpolation processing, a third stepof performing super-resolution processing, and a fourth step ofperforming overdrive processing, is provided. The third step isperformed after the first step or the second step. The fourth step isperformed after the third step.

Alternatively, a method for driving a semiconductor device, whichincludes a first step of performing edge enhancement processing, asecond step of performing frame interpolation processing, a third stepof performing super-resolution processing, a fourth step of performinglocal dimming processing, and a fifth step of performing overdriveprocessing, is provided. The third step is performed after the firststep or the second step. The fourth step is performed after the thirdstep. The fifth step is performed after the fourth step.

Note that a variety of switches can be used as a switch. For example, anelectrical switch, a mechanical switch, or the like can be used as aswitch. That is, any element can be used as a switch as long as it cancontrol current, without limitation to a certain element. For example, atransistor (e.g., a bipolar transistor or a MOS transistor), a diode(e.g., a PN diode, a PIN diode, a Schottky diode, an MIM (metalinsulator metal) diode, an MIS (metal insulator semiconductor) diode, ora diode-connected transistor), a logic circuit in which such elementsare combined, or the like can be used as a switch. An example of amechanical switch is a switch formed using a MEMS (micro electromechanical system) technology, such as a digital micromirror device(DMD). Such a switch includes an electrode which can be movedmechanically, and operates by controlling conduction and non-conductionin accordance with movement of the electrode.

In the case of using a transistor as a switch, the polarity(conductivity type) of the transistor is not particularly limited to acertain type because it operates just as a switch. However, a transistorhaving polarity with smaller off-state current is preferably used whenthe amount of off-state current is to be suppressed. Examples of atransistor with smaller off-state current are a transistor provided withan LDD region, a transistor with a multi-gate structure, and the like.

Note that in the case of using a transistor as a switch, an n-channeltransistor is preferably used as the switch when a potential of a sourceof the transistor which is operated as the switch is close to apotential of a low-potential-side power supply (e.g., Vss, GND, or 0 V).On the other hand, a p-channel transistor is preferably used as theswitch when the potential of the source is close to a potential of ahigh-potential-side power supply (e.g., Vdd). This is because theabsolute value of gate-source voltage can be increased when thepotential of the source of the n-channel transistor is close to apotential of a low-potential-side power supply and when the potential ofthe source of the p-channel transistor is close to a potential of ahigh-potential-side power supply, so that the transistor can be moreaccurately operated as a switch. Alternatively, this is because thetransistor does not often perform source follower operation, so that thedecrease in output voltage does not often occur.

Note that a CMOS switch may be used as a switch with the use of both ann-channel transistor and a p-channel transistor. By using a CMOS switch,the switch can be more accurately operated as a switch because currentcan flow when either the p-channel transistor or the n-channeltransistor is turned on. Thus, voltage can be appropriately outputregardless of whether voltage of an input signal to the switch is highor low. Alternatively, since the voltage amplitude value of a signal forturning on or off the switch can be made small, power consumption can bereduced.

Note that when a transistor is used as a switch, the switch includes aninput terminal (one of a source and a drain), an output terminal (theother of the source and the drain), and a terminal for controllingconduction (a gate) in some cases. On the other hand, when a diode isused as a switch, the switch does not include a terminal for controllingconduction in some cases. Therefore, when a diode is used as a switch,the number of wirings for controlling terminals can be further reducedas compared to the case of using a transistor.

Note that a display element, a display device which is a deviceincluding a display element, a light-emitting element, and alight-emitting device which is a device including a light-emittingelement can employ various modes and can include various elements. Forexample, a display medium, whose contrast, luminance, reflectivity,transmittance, or the like changes by electromagnetic action, such as anEL (electroluminescence) element (e.g., an EL element including organicand inorganic materials, an organic EL element, or an inorganic ELelement), an LED (e.g., a white LED, a red LED, a green LED, or a blueLED), a transistor (a transistor which emits light depending on theamount of current), an electron emitter, a liquid crystal element,electronic ink, an electrophoretic element, a grating light valve (GLV),a plasma display panel (PDP), a digital micromirror device (DMD), apiezoelectric ceramic display, or a carbon nanotube, can be used as adisplay element, a display device, a light-emitting element, or alight-emitting device. Display devices having EL elements include an ELdisplay and the like. Display devices having electron emitters include afield emission display (FED), an SED-type flat panel display (SED:surface-conduction electron-emitter display), and the like. Displaydevices having liquid crystal elements include a liquid crystal display(e.g., a transmissive liquid crystal display, a transflective liquidcrystal display, a reflective liquid crystal display, a direct-viewliquid crystal display, or a projection liquid crystal display) and thelike. Display devices having electronic ink or electrophoretic elementsinclude electronic paper and the like.

Examples of an EL element are an element including an anode, a cathode,and an EL layer interposed between the anode and the cathode, and thelike. Examples of an EL layer are a layer utilizing light emission(fluorescence) from a singlet exciton, a layer utilizing light emission(phosphorescence) from a triplet exciton, a layer utilizing lightemission (fluorescence) from a singlet exciton and light emission(phosphorescence) from a triplet exciton, a layer formed using anorganic material, a layer formed using an inorganic material, a layerformed using an organic material and an inorganic material, a layerincluding a high-molecular material, a layer including a low-molecularmaterial, a layer including a high-molecular material and alow-molecular material, and the like. Note that the present invention isnot limited to this, and a variety of EL elements can be used as an ELelement.

Examples of an electron emitter are an element in which electrons areextracted by high electric field concentration on a cathode, and thelike. Specifically, examples of an electron emitter are a Spindt type, acarbon nanotube (CNT) type, a metal-insulator-metal (MIM) type in whicha metal, an insulator, and a metal are stacked, ametal-insulator-semiconductor (MIS) type in which a metal, an insulator,and a semiconductor are stacked, a MOS type, a silicon type, a thin filmdiode type, a diamond type, a thin film type in which a metal, aninsulator, a semiconductor, and a metal are stacked, a HEED type, an ELtype, a porous silicon type, a surface-conduction (SCE) type, and thelike. Note that the present invention is not limited to this, and avariety of elements can be used as an electron emitter.

For example, an element which controls transmission or non-transmissionof light by optical modulation action of liquid crystals can be used asa liquid crystal element. The element can include a pair of electrodesand liquid crystals. Note that the optical modulation action of liquidcrystals is controlled by an electric field applied to the liquidcrystals (including a horizontal electric field, a vertical electricfield, and a diagonal electric field). Note that specifically, thefollowing can be used for a liquid crystal element, for example: anematic liquid crystal, a cholesteric liquid crystal, a smectic liquidcrystal, a discotic liquid crystal, a thermotropic liquid crystal, alyotropic liquid crystal, a low-molecular liquid crystal, ahigh-molecular liquid crystal, a polymer dispersed liquid crystal(PDLC), a ferroelectric liquid crystal, an anti-ferroelectric liquidcrystal, a main-chain liquid crystal, a side-chain high-molecular liquidcrystal, a plasma addressed liquid crystal (PALO), a banana-shapedliquid crystal, and the like. In addition, the following can be used asa diving method of a liquid crystal: a TN (twisted nematic) mode, an STN(super twisted nematic) mode, an IPS (in-plane-switching) mode, an FFS(fringe field switching) mode, an MVA (multi-domain vertical alignment)mode, a PVA (patterned vertical alignment) mode, an ASV (advanced superview) mode, an ASM (axially symmetric aligned macrocell) mode, an OCB(optically compensated birefringence) mode, an ECB (electricallycontrolled birefringence) mode, an ITC (ferroelectric liquid crystal)mode, an AFLC (anti-ferroelectric liquid crystal) mode, a PDLC (polymerdispersed liquid crystal) mode, a guest-host mode, a blue phase mode,and the like. Note that the present invention is not limited to this,and a variety of liquid crystal elements and driving methods thereof canbe used as a liquid crystal element and a driving method thereof.

For example, a device for displaying images by molecules (a device whichutilizes optical anisotropy, dye molecular orientation, or the like), adevice for displaying images by particles (a device which utilizeselectrophoresis, particle movement, particle rotation, phase change, orthe like), a device for displaying images by movement of one end of afilm, a device for displaying images by using coloring properties orphase change of molecules, a device for displaying images by usingoptical absorption by molecules, a device for displaying images by usingself-light emission by combination of electrons and holes, or the likecan be used as electronic paper. Specifically, examples of a displaymethod of electronic paper are microcapsule electrophoresis, horizontalelectrophoresis, vertical electrophoresis, a spherical twisting ball, amagnetic twisting ball, a columnar twisting ball, a charged toner, anelectron powder and granular material, magnetic electrophoresis, amagnetic thermosensitive type, electro wetting, light-scattering(transparent-opaque change), a cholesteric liquid crystal and aphotoconductive layer, a cholesteric liquid crystal, a bistable nematicliquid crystal, a ferroelectric liquid crystal, a liquid crystaldispersed type with a dichroic dye, a movable film, coloring anddecoloring properties of a leuco dye, photochromism, electrochromism,electrodeposition, flexible organic EL, and the like. Note that thepresent invention is not limited to this, and a variety of electronicpaper and display methods thereof can be used as electronic paper and adriving method thereof. Here, by using microcapsule electrophoresis,defects of electrophoresis, which are aggregation and precipitation ofphoresis particles, can be solved. Electron powder and granular materialhas advantages such as high-speed response, high reflectivity, wideviewing angle, low power consumption, and memory properties.

Examples of a plasma display panel are a plasma display panel which hasa structure where a substrate having a surface provided with anelectrode faces a substrate having a surface provided with an electrodeand a minute groove in which a phosphor layer is formed at a narrowinterval and a rare gas is sealed therein, and the like. In addition,different examples of a plasma display panel are a plasma display panelwhich has a structure where a plasma tube is sandwiched betweenfilm-form electrodes from the top and the bottom, and the like. Theplasma tube is formed by sealing a discharge gas, RGB fluorescentmaterials, and the like inside a glass tube. Note that the plasmadisplay panel can perform display by application of voltage between theelectrodes to generate an ultraviolet ray so that a phosphor emitslight. Note that examples of a plasma display panel are a DC-type PDP,an AC-type PDP, and the like. Here, as a driving method of the plasmadisplay panel, AWS (address while sustain) driving, ADS (address displayseparated) driving in which a subframe is divided into a reset period,an address period, and a sustain period, CLEAR (high-contrast and lowenergy address and reduction of false contour sequence) driving, ALIS(alternate lighting of surfaces) method, TERES (technology of reciprocalsustainer) driving, or the like can be used. Note that the presentinvention is not limited to this, and a variety of plasma display panelscan be used.

Note that electroluminescence, a cold cathode fluorescent lamp, a hotcathode fluorescent lamp, an LED, a laser light source, a mercury lamp,or the like can be used as a light source of a display device in which alight source is needed, such as a liquid crystal display (e.g., atransmissive liquid crystal display, a transflective liquid crystaldisplay, a reflective liquid crystal display, a direct-view liquidcrystal display, or a projection liquid crystal display), a displaydevice including a grating light valve (GLV), or a display deviceincluding a digital micromirror device (DMD), for example. Note that thepresent invention is not limited to this, and a variety of light sourcescan be used as a light source.

Note that transistors with a variety of structures can be used as atransistor, without limitation to a certain type. For example, a thinfilm transistor (TFT) including a non-single-crystal semiconductor filmtypified by amorphous silicon, polycrystalline silicon, microcrystalline(also referred to as microcrystal, nanocrystal, or semi-amorphous)silicon, or the like can be used as a transistor. In the case of usingthe TFT, there are various advantages. For example, since the TFT can beformed at temperature which is lower than that of the case of usingsingle crystal silicon, manufacturing cost can be reduced or amanufacturing apparatus can be made large. Since the manufacturingapparatus can be made large, the TFT can be formed using a largesubstrate. Therefore, many display devices can be formed concurrently atlow cost. Alternatively, since the manufacturing temperature is low, asubstrate having low heat resistance can be used. Therefore, thetransistor can be formed using a light-transmitting substrate.Alternatively, transmission of light in a display element can becontrolled by using the transistor formed using the light-transmittingsubstrate. Alternatively, part of a film included in the transistor cantransmit light because the thickness of the transistor is small.Therefore, the aperture ratio can be improved.

Note that by using a catalyst (e.g., nickel) in the case of formingpolycrystalline silicon, crystallinity can be further improved and atransistor having excellent electrical characteristics can be formed.Accordingly, a gate driver circuit (e.g., a scan line driver circuit), asource driver circuit (e.g., a signal line driver circuit), and a signalprocessing circuit (e.g., a signal generation circuit, a gammacorrection circuit, or a DA converter circuit) can be formed using thesame substrate as a pixel portion.

Note that by using a catalyst (e.g., nickel) in the case of formingmicrocrystalline silicon, crystallinity can be further improved and atransistor having excellent electrical characteristics can be formed. Inthis case, crystallinity can be improved by just performing heattreatment without performing laser irradiation. Accordingly, a gatedriver circuit (e.g., a scan line driver circuit) and part of a sourcedriver circuit (e.g., an analog switch) can be formed using the samesubstrate as a pixel portion. Note that in the case where laserirradiation for crystallization is not performed, unevenness incrystallinity of silicon can be suppressed. Therefore, high-qualityimages can be displayed. Note that polycrystalline silicon ormicrocrystalline silicon can be formed without use of a catalyst (e.g.,nickel).

Note that it is preferable that crystallinity of silicon be improved topolycrystal, microcrystal, or the like in the whole panel; however, thepresent invention is not limited to this. Crystallinity of silicon maybe improved only in part of the panel. Selective improvement incrystallinity is possible by selective laser irradiation or the like.For example, only a peripheral driver circuit region excluding pixelsmay be irradiated with laser light. Alternatively, only a region of agate driver circuit, a source driver circuit, or the like may beirradiated with laser light. Alternatively, only part of a source drivercircuit (e.g., an analog switch) may be irradiated with laser light.Accordingly, crystallinity of silicon can be improved only in a regionin which a circuit needs to be operated at high speed. Since a pixelregion is not particularly needed to be operated at high speed, even ifcrystallinity is not improved, the pixel circuit can be operated withoutproblems. Thus, a region whose crystallinity is improved is small, sothat manufacturing steps can be decreased. Thus, throughput can beincreased and manufacturing cost can be reduced. Alternatively, sincethe number of necessary manufacturing apparatus is small, manufacturingcost can be reduced.

Note that for example, a transistor including a compound semiconductoror an oxide semiconductor, such as ZnO, a-InGaZnO, SiGe, GaAs, IZO, ITO,SnO, TiO, or AIZnSnO (AZTO), a thin film transistor obtained by thinningsuch a compound semiconductor or an oxide semiconductor, or the like canbe used as a transistor. Thus, manufacturing temperature can be loweredand, for example, such a transistor can be formed at room temperature.Accordingly, the transistor can be formed directly on a substrate havinglow heat resistance, such as a plastic substrate or a film substrate.Note that such a compound semiconductor or an oxide semiconductor can beused not only for a channel portion of the transistor but also for otherapplications. For example, such a compound semiconductor or an oxidesemiconductor can be used for a wiring, a resistor, a pixel electrode, alight-transmitting electrode, or the like. Since such an element can beformed at the same time as the transistor, cost can be reduced.

Note that for example, a transistor or the like formed by an inkjetmethod or a printing method can be used as a transistor. Thus, atransistor can be formed at room temperature, can be formed at a lowvacuum, or can be formed using a large substrate. Therefore, thetransistor can be formed without use of a mask (reticle), so that thelayout of the transistor can be easily changed. Alternatively, since thetransistor can be formed without use of a resist, material cost isreduced and the number of steps can be reduced. Alternatively, since afilm can be formed where needed, a material is not wasted as compared toa manufacturing method by which etching is performed after the film isformed over the entire surface, so that cost can be reduced.

Note that for example, a transistor or the like including an organicsemiconductor or a carbon nanotube can be used as a transistor. Thus,such a transistor can be formed over a flexible substrate. Asemiconductor device formed using such a substrate can resist shocks.

Note that transistors with a variety of different structures can be usedas a transistor. For example, a MOS transistor, a junction transistor, abipolar transistor, or the like can be used as a transistor. By using aMOS transistor as a transistor, the size of the transistor can bereduced. Thus, a large number of transistors can be mounted. By using abipolar transistor as a transistor, a large amount of current can flow.Thus, a circuit can be operated at high speed. Note that a MOStransistor and a bipolar transistor may be formed over one substrate.Thus, reduction in power consumption, reduction in size, high-speedoperation, and the like can be achieved.

Note that for example, a transistor with a multi-gate structure havingtwo or more gate electrodes can be used as a transistor. With themulti-gate structure, a structure where a plurality of transistors areconnected in series is provided because channel regions are connected inseries. Thus, with the multi-gate structure, the amount of off-statecurrent can be reduced and the withstand voltage of the transistor canbe increased (reliability can be improved). Alternatively, with themulti-gate structure, drain-source current does not fluctuate very mucheven when drain-source voltage fluctuates when the transistor operatesin a saturation region, so that a flat slope of voltage-currentcharacteristics can be obtained. By utilizing the flat slope of thevoltage-current characteristics, an ideal current source circuit or anactive load having an extremely large resistance value can be realized.Accordingly, a differential circuit, a current mirror circuit, or thelike having excellent properties can be realized.

Note that for example, a transistor with a structure where gateelectrodes are formed above and below a channel can be used as atransistor. With the structure where the gate electrodes are formedabove and below the channel, a circuit structure where a plurality oftransistors are connected in parallel is provided. Thus, a channelregion is increased, so that the amount of current can be increased.Alternatively, with the structure where gate electrodes are formed aboveand below the channel, a depletion layer can be easily formed, so thatsubthreshold swing can be improved.

Note that for example, a transistor with a structure where a gateelectrode is formed above a channel region, a structure where a gateelectrode is formed below a channel region, a staggered structure, aninverted staggered structure, a structure where a channel region isdivided into a plurality of regions, a structure where channel regionsare connected in parallel or in series, or the like can be used as atransistor.

Note that for example, a transistor with a structure where a sourceelectrode or a drain electrode overlaps with a channel region (or partof it) can be used as a transistor. With the structure where the sourceelectrode or the drain electrode overlaps with the channel region (orpart of it), unstable operation due to accumulation of electric chargein part of the channel region can be prevented.

Note that for example, a transistor with a structure where an LDD regionis provided can be used as a transistor. By providing the LDD region,the amount of off-state current can be reduced or the withstand voltageof the transistor can be increased (reliability can be improved).Alternatively, by providing the LDD region, drain-source current doesnot fluctuate very much even when drain-source voltage fluctuates whenthe transistor operates in the saturation region, so that a flat slopeof voltage-current characteristics can be obtained.

Note that a transistor can be formed using a variety of substrates,without limitation to a certain type. As the substrate, a semiconductorsubstrate (e.g., a single crystal substrate or a silicon substrate), anSOI substrate, a glass substrate, a quartz substrate, a plasticsubstrate, a metal substrate, a stainless steel substrate, a substrateincluding stainless steel foil, a tungsten substrate, a substrateincluding tungsten foil, a flexible substrate, an attachment film, paperincluding a fibrous material, a base material film, or the like can beused, for example. As a glass substrate, a barium borosilicate glasssubstrate, an aluminoborosilicate glass substrate, a soda-lime glasssubstrate, or the like can be used, for example. For a flexiblesubstrate, a flexible synthetic resin such as plastics typified bypolyethylene terephthalate (PET), polyethylene naphthalate (PEN), orpolyether sulfone (PES), or acrylic can be used, for example. For anattachment film, polypropylene, polyester, vinyl, polyvinyl fluoride,polyvinyl chloride, or the like can be used, for example. For a basematerial film, polyester, polyimide, polyimide, an inorganic vapordeposition film, paper, or the like can be used, for example. Inparticular, by forming transistors with the use of a semiconductorsubstrate, a single crystal substrate, an SOI substrate, or the like,transistors with fewer variations in characteristics, sizes, shapes, orthe like, with high current supply capability, and with small sizes canbe formed. By forming a circuit with the use of such a transistor, powerconsumption of the circuit can be reduced or the circuit can be highlyintegrated.

Note that the transistor may be formed using one substrate, and then,the transistor may be transferred to another substrate. In addition tothe above substrates over which the transistor can be formed, a papersubstrate, a cellophane substrate, a stone substrate, a wood substrate,a cloth substrate (including a natural fiber (e.g., silk, cotton, orhemp), a synthetic fiber (e.g., nylon, polyurethane, or polyester), aregenerated fiber (e.g., acetate, cupra, rayon, or regeneratedpolyester), or the like), a leather substrate, a rubber substrate, orthe like can be used as a substrate to which the transistor istransferred. By using such a substrate, a transistor with excellentproperties or a transistor with low power consumption can be formed, adevice with high durability and high heat resistance can be provided, orreduction in weight or thickness can be achieved.

Note that all the circuits that are necessary to realize a predeterminedfunction can be formed using the same substrate (e.g., a glasssubstrate, a plastic substrate, a single crystal substrate, or an SOIsubstrate). Thus, cost can be reduced by reduction in the number ofcomponents or reliability can be improved by reduction in the number ofconnections to circuit components.

Note that it is possible not to form all the circuits that are necessaryto realize the predetermined function over the same substrate. That is,some of the circuits which are necessary to realize the predeterminedfunction can be formed using one substrate and some of the circuitswhich are necessary to realize the predetermined function can be formedusing another substrate. For example, some of the circuits which arenecessary to realize the predetermined function can be formed using aglass substrate and some of the circuits which are necessary to realizethe predetermined function can be formed using a single crystalsubstrate (or an SOI substrate). The single crystal substrate over whichsome of the circuits which are necessary to realize the predeterminedfunction (such a substrate is also referred to as an IC chip) can beconnected to the glass substrate by COG (chip on glass), and the IC chipcan be provided over the glass substrate. Alternatively, the IC chip canbe connected to the glass substrate by TAB (tape automated bonding), COF(chip on film), SMT (surface mount technology), a printed circuit board,or the like. When some of the circuits are formed using the samesubstrate as a pixel portion in this manner, cost can be reduced byreduction in the number of components or reliability can be improved byreduction in the number of connections to circuit components. Inparticular, a circuit with high driving voltage, a circuit with highdriving frequency, or the like consumes a large amount of power in manycases. Thus, such a circuit is formed using a substrate which isdifferent from the substrate over which the pixel portion is formed(e.g., a single crystal substrate), and an IC chip is formed. With theIC chip, the increase in power consumption can be prevented.

Note that one pixel corresponds to the minimum unit of an image.Accordingly, in the case of a full color display device having colorelements of R (red), G (green), and B (blue), one pixel includes a dotof the color element of R, a dot of the color element of G, and a dot ofthe color element of B. Note that the color elements are not limited tothree colors, and color elements of more than three colors may be usedor a color other than RGB may be used. For example, RGBW (W correspondsto white) can be used by addition of white. Alternatively, one or morecolors of yellow, cyan, magenta, emerald green, vermilion, and the likemay be added to RGB, for example. Alternatively, a color which issimilar to at least one of R, G, and B may be added to RGB, for example.For example, R, G, B1, and B2 may be used. Although both B1 and B2 areblue, they have slightly different wavelengths. In a similar manner, R1,R2, G, and B may be used. By using such color elements, display which iscloser to the real object can be performed or power consumption can bereduced. Note that one pixel may include a plurality of dots of colorelements of the same color. In this case, the plurality of colorelements may have different sizes of regions which contribute todisplay. Alternatively, by separately controlling the plurality of dotsof color elements of the same color, gradation may be expressed. Thismethod is referred to as an area-ratio gray scale method. Alternatively,by using the plurality of dots of color elements of the same color,signals supplied to each of the plurality of dots may be slightly variedso that the viewing angle is widened. That is, potentials of pixelelectrodes included in the plurality of color elements of the same colormay be different from each other. Accordingly, voltage applied to liquidcrystal molecules are varied depending on the pixel electrodes.Therefore, the viewing angle can be widened.

Note that pixels are provided (arranged) in matrix in some cases. Here,description that pixels are provided (arranged) in matrix includes thecase where the pixels are arranged in a straight line and the case wherethe pixels are arranged in a jagged line, in a longitudinal direction ora lateral direction. Thus, for example, in the case of performing fullcolor display with three color elements (e.g., RGB), the following casesare included: the case where the pixels are arranged in stripes, thecase where dots of the three color elements are arranged in a deltapattern, and the case where dots of the three color elements areprovided in Bayer arrangement. Note that the size of display regions maybe different between dots of color elements. Thus, power consumption canbe reduced or the life of a display element can be prolonged.

Note that an active matrix method in which an active element is includedin a pixel or a passive matrix method in which an active element is notincluded in a pixel can be used.

In an active matrix method, as an active element (a non-linear element),not only a transistor but also a variety of active elements (non-linearelements) can be used. For example, an MIM (metal insulator metal), aTFD (thin film diode), or the like can also be used. Since such anelement has a small number of manufacturing steps, manufacturing costcan be reduced or yield can be improved. Alternatively, since the sizeof the element is small, the aperture ratio can be improved, so thatpower consumption can be reduced or higher luminance can be achieved.

As a method other than the active matrix method, a passive matrix methodin which an active element (a non-linear element) is not used can beused. Since an active element (a non-linear element) is not used, thenumber of manufacturing steps is small, so that manufacturing cost canbe reduced or yield can be improved. Alternatively, since an activeelement (a non-linear element) is not used, the aperture ratio can beimproved, so that power consumption can be reduced or higher luminancecan be achieved, for example.

Note that a transistor is an element having at least three terminals: agate, a drain, and a source. The transistor has a channel region betweena drain region and a source region, and current can flow through thedrain region, the channel region, and the source region. Here, since thesource and the drain of the transistor change depending on thestructure, the operating condition, and the like of the transistor, itis difficult to define which is a source or a drain. Thus, a regionwhich serves as a source or a region which serves as a drain is notreferred to as a source or a drain in some cases. In that case, one ofthe source and the drain might be referred to as a first terminal, afirst electrode, or a first region, and the other of the source and thedrain might be referred to as a second terminal, a second electrode, ora second region, for example.

Note that a transistor may be an element having at least threeterminals: a base, an emitter, and a collector. Also in this case, oneof the emitter and the collector might be referred to as a firstterminal, a first electrode, or a first region, and the other of theemitter and the collector might be referred to as a second terminal, asecond electrode, or a second region, for example. Note that in the casewhere a bipolar transistor is used as the transistor, the term “gate”can be replaced with the term “base”.

Note that a semiconductor device corresponds to a device having acircuit including a semiconductor element (e.g., a transistor, a diode,or a thyristor). The semiconductor device may correspond to also alldevices that can function by utilizing semiconductor characteristics anda device having a semiconductor material.

Note that a display device corresponds to a device having a displayelement. The display device may include a plurality of pixels eachhaving a display element. Note that that the display device may includea peripheral driver circuit for driving the plurality of pixels. Theperipheral driver circuit for driving the plurality of pixels may beformed using the same substrate as the plurality of pixels. The displaydevice may include a peripheral driver circuit provided over a substrateby wire bonding or bump bonding, namely, an IC chip connected by chip onglass (COG) or an IC chip connected by TAB or the like. The displaydevice may include a flexible printed circuit (FPC) to which an IC chip,a resistor, a capacitor, an inductor, a transistor, or the like isattached. Note that the display device may include a printed wiringboard (PWB) which is connected through a flexible printed circuit (FPC)and to which an IC chip, a resistor, a capacitor, an inductor, atransistor, or the like is attached. The display device may include anoptical sheet such as a polarizing plate or a retardation plate. Thedisplay device may include a lighting device, a housing, an audio inputand output device, an optical sensor, or the like.

Note that a lighting device may include a backlight unit, a light guideplate, a prism sheet, a diffusion sheet, a reflective sheet, a lightsource (e.g., an LED or a cold cathode fluorescent lamp), a coolingdevice (e.g., a water cooling device or an air cooling device), or thelike.

Note that a light-emitting device corresponds to a device having alight-emitting element or the like. In the case where a light-emittingdevice includes a light-emitting element as a display element, thelight-emitting device is one of specific examples of a display device.

Note that a reflective device corresponds to a device having alight-reflective element, a light diffraction element, light-reflectiveelectrode, or the like.

Note that a liquid crystal display device corresponds to a displaydevice including a liquid crystal element. Liquid crystal displaydevices include a direct-view liquid crystal display, a projectionliquid crystal display, a transmissive liquid crystal display, areflective liquid crystal display, a transflective liquid crystaldisplay, and the like.

Note that a driving device corresponds to a device having asemiconductor element, an electric circuit, or an electronic circuit.For example, a transistor which controls input of signals from a sourcesignal line to pixels (also referred to as a selection transistor, aswitching transistor, or the like), a transistor which supplies voltageor current to a pixel electrode, a transistor which supplies voltage orcurrent to a light-emitting element, and the like are examples of thedriving device. A circuit which supplies signals to a gate signal line(also referred to as a gate driver, a gate line driver circuit, or thelike), a circuit which supplies signals to a source signal line (alsoreferred to as a source driver, a source line driver circuit, or thelike), and the like are also examples of the driving device.

Note that a display device, a semiconductor device, a lighting device, acooling device, a light-emitting device, a reflective device, a drivingdevice, and the like overlap with each other in some cases. For example,a display device includes a semiconductor device and a light-emittingdevice in some cases. Alternatively, a semiconductor device includes adisplay device and a driving device in some cases.

Note that when it is explicitly described that “A and B are connected”,the case where A and B are electrically connected, the case where A andB are functionally connected, and the case where A and B are directlyconnected are included therein. Here, each of A and B is an object(e.g., a device, an element, a circuit, a wiring, an electrode, aterminal, a conductive film, or a layer). Accordingly, another elementmay be interposed between elements having a connection relationillustrated in drawings and texts, without limitation to a predeterminedconnection relation, for example, the connection relation illustrated inthe drawings and the texts.

For example, in the case where A and B are electrically connected, oneor more elements which enable electrical connection between A and B(e.g., a switch, a transistor, a capacitor, an inductor, a resistor,and/or a diode) can be connected between A and B.

For example, in the case where A and B are functionally connected, oneor more circuits which enable functional connection between A and B(e.g., a logic circuit such as an inverter, a NAND circuit, or a NORcircuit; a signal converter circuit such as a DA converter circuit, anAD converter circuit, or a gamma correction circuit; a potential levelconverter circuit such as a power supply circuit (e.g., a dc-dcconverter, a step-up dc-dc converter, or a step-down dc-dc converter) ora level shifter circuit for changing a potential level of a signal; avoltage source; a current source; a switching circuit; an amplifiercircuit such as a circuit which can increase signal amplitude, theamount of current, or the like, an operational amplifier, a differentialamplifier circuit, a source follower circuit, or a buffer circuit; asignal generation circuit; a memory circuit; and/or a control circuit)can be connected between A and B. Note that for example, in the casewhere a signal output from A is transmitted to B even when anothercircuit is interposed between A and B, A and B are functionallyconnected.

Note that when it is explicitly described that “A and B are electricallyconnected”, the case where A and B are electrically connected (i.e., thecase where A and B are connected with another element or another circuitinterposed therebetween), the case where A and B are functionallyconnected (i.e., the case where A and B are functionally connected withanother circuit interposed therebetween), and the case where A and B aredirectly connected (i.e. the case where A and B are connected withoutanother element or another circuit interposed therebetween) are includedtherein. That is, when it is explicitly described that “A and B areelectrically connected”, the description is the same as the case whereit is explicitly only described that “A and B are connected”.

Note that when it is explicitly described that “B is formed on A” or “Bis formed over A”, it does not necessarily mean that B is formed indirect contact with A. The description includes the case where A and Bare not in direct contact with each other, i.e., the case where anotherobject is interposed between A and B. Here, each of A and B is an object(e.g., a device, an element, a circuit, a wiring, an electrode, aterminal, a conductive film, or a layer).

Accordingly, for example, when it is explicitly described that “a layerB is formed on (or over) a layer A”, it includes both the case where thelayer B is formed in direct contact with the layer A, and the case whereanother layer (e.g., a layer C or a layer D) is formed in direct contactwith the layer A and the layer B is formed in direct contact with thelayer C or the layer D. Note that another layer (e.g., a layer C or alayer D) may be a single layer or a plurality of layers.

In a similar manner, when it is explicitly described that “B is formedabove A”, it does not necessarily mean that B is formed in directcontact with A, and another object may be interposed therebetween. Thus,for example, when it is described that “a layer B is formed above alayer A”, it includes both the case where the layer B is formed indirect contact with the layer A, and the case where another layer (e.g.,a layer C or a layer D) is formed in direct contact with the layer A andthe layer B is formed in direct contact with the layer C or the layer D.Note that another layer (e.g., a layer C or a layer D) may be a singlelayer or a plurality of layers.

Note that when it is explicitly described that “B is formed on A”, “B isformed over A”, or “B is formed above A”, it includes the case where Bis formed obliquely over/above A.

Note that the same can be said when it is described that “B is formedunder A” or “B is formed below A”.

Note that when an object is explicitly described in a singular form, theobject is preferably singular. Note that the present invention is notlimited to this, and the object can be plural. In a similar manner, whenan object is explicitly described in a plural form, the object ispreferably plural. Note that the present invention is not limited tothis, and the object can be singular.

Note that size, the thickness of layers, or regions in the drawings areexaggerated for simplicity in some cases. Thus, embodiments of thepresent invention are not limited to such scales illustrated in thedrawings.

Note that the drawings are perspective views of ideal examples, andshapes or values are not limited to those illustrated in the drawings.For example, the following can be included: variation in shape due to amanufacturing technique; variation in shape due to an error; variationin signal, voltage, or current due to noise; variation in signal,voltage, or current due to a difference in timing: or the like.

Note that technical terms are used in order to describe a specificembodiment, example, or the like in many cases. However, one embodimentof the present invention should not be construed as being limited by thetechnical terms.

Note that terms which are not defined (including terms used for scienceand technology, such as technical terms or academic parlance) can beused as terms which have meaning equal to general meaning that anordinary person skilled in the art understands. It is preferable thatterms defined by dictionaries or the like be construed as consistentmeaning with the background of related art.

Note that terms such as “first”, “second”, “third”, and the like areused for distinguishing various elements, members, regions, layers, andareas from others. Therefore, the terms such as “first”, “second”,“third”, and the like do not limit the number of the elements, members,regions, layers, areas, or the like. Further, for example, the term“first” can be replaced with the term “second”, “third”, or the like.

Note that terms for describing spatial arrangement, such as “over”,“above”, “under”, “below”, “laterally”, “right”, “left”, “obliquely”,“behind”, “front”, “inside”, “outside”, and “in” are often used forbriefly showing a relationship between an element and another element orbetween a feature and another feature with reference to a diagram. Notethat embodiments of the present invention are not limited to this, andsuch terms for describing spatial arrangement can indicate not only thedirection illustrated in a diagram but also another direction. Forexample, when it is explicitly described that “B is over A”, it does notnecessarily mean that B is placed over A, and can include the case whereB is placed under A because a device in a diagram can be inverted orrotated by 180°. Accordingly, “over” can refer to the directiondescribed by “under” in addition to the direction described by “over”.Note that embodiments of the present invention are not limited to this,and “over” can refer to any of the other directions described by“laterally”, “right”, “left”, “obliquely”, “behind”, “front”, “inside”,“outside”, and “in” in addition to the directions described by “over”and “under” because the device in the diagram can be rotated in avariety of directions. That is, the terms for describing spatialarrangement can be construed adequately depending on the situation.

According to one embodiment of the present invention, image quality canbe improved.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIGS. 1A and 1B illustrate flows according to one example of anembodiment;

FIGS. 2A to 2D illustrate flows according to one example of theembodiment;

FIGS. 3A to 3D illustrate flows according to one example of theembodiment;

FIGS. 4A to 4C show display screens according to one example of anembodiment;

FIGS. 5A to 5C illustrate flows according to one example of theembodiment;

FIGS. 6A and 6B illustrate flows according to one example of theembodiment;

FIGS. 7A to 7C illustrate flows according to one example of theembodiment;

FIGS. 8A to 8C illustrate circuits according to one example of theembodiment;

FIGS. 9A to 9D illustrate flows according to one example of anembodiment;

FIGS. 10A to 10C illustrate flows according to one example of theembodiment;

FIGS. 11A and 11B illustrate flows according to one example of theembodiment;

FIGS. 12A and 12B illustrate flows according to one example of theembodiment;

FIGS. 13A and 13B illustrate flows according to one example of anembodiment;

FIGS. 14A and 14B illustrate flows according to one example of theembodiment;

FIGS. 15A and 15B illustrate flows according to one example of theembodiment;

FIGS. 16A and 16B illustrate flows according to one example of theembodiment;

FIG. 17A is a top view illustrating a device according to one example ofan embodiment, and FIG. 17B is a cross-sectional view illustrating thedevice;

FIGS. 18A and 18C are top views illustrating a device according to oneexample of the embodiment, and FIGS. 18B and 18D are cross-sectionalviews illustrating the device;

FIGS. 19A, 19C, and 19E show voltage of a display element according toone example of an embodiment, and FIGS. 19B, 19D, and 19F showtransmittance of the display element;

FIGS. 20A to 20C show display screens according to one example of anembodiment;

FIGS. 21A to 21G illustrate circuits according to one example of anembodiment;

FIGS. 22A to 22H illustrate circuits according to one example of theembodiment;

FIGS. 23A and 23B illustrate structures of display devices according toone example of an embodiment;

FIGS. 24A to 24E illustrate structures of display devices according toone example of the embodiment;

FIGS. 25A to 25C are cross-sectional views illustrating structures oftransistors according to one example of an embodiment;

FIGS. 26A to 26H illustrate electronic devices according to one exampleof an embodiment; and

FIGS. 27A to 27H illustrate electronic devices according to one exampleof the embodiment.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, embodiments will be described with reference to thedrawings. Note that the embodiments can be implemented in variousdifferent ways and it will be readily appreciated by those skilled inthe art that modes and details of the embodiments can be changed invarious ways without departing from the spirit and scope of the presentinvention. Therefore, the present invention should not be construed asbeing limited to the following description of the embodiments. Note thatin structures described below, the same portions or portions havingsimilar functions are denoted by common reference numerals in differentdrawings, and description thereof is not repeated.

Note that a content (or may be part of the content) described in oneembodiment may be applied to, combined with, or replaced by a differentcontent (or may be part of the different content) described in theembodiment and/or a content (or may be part of the content) described inone or a plurality of different embodiments.

Note that in each embodiment, a content described in the embodiment is acontent described with reference to a variety of diagrams or a contentdescribed with a text described in this specification.

Note that by combining a diagram (or may be part of the diagram)illustrated in one embodiment with another part of the diagram, adifferent diagram (or may be part of the different diagram) illustratedin the embodiment, and/or a diagram (or may be part of the diagram)illustrated in one or a plurality of different embodiments, much morediagrams can be formed.

Note that in a diagram or a text described in one embodiment, part ofthe diagram or the text is taken out, and one embodiment of theinvention can be constituted. Thus, in the case where a diagram or atext related to a certain portion is described, the context taken outfrom part of the diagram or the text is also disclosed as one embodimentof the invention, and one embodiment of the invention can beconstituted. Therefore, for example, in a diagram (e.g., across-sectional view, a plan view, a circuit diagram, a block diagram, aflow chart, a process diagram, a perspective view, a cubic diagram, alayout diagram, a timing chart, a structure diagram, a schematic view, agraph, a list, a ray diagram, a vector diagram, a phase diagram, awaveform chart, a photograph, or a chemical formula) or a text in whichone or more active elements (e.g., transistors or diodes), wirings,passive elements (e.g., capacitors or resistors), conductive layers,insulating layers, semiconductor layers, organic materials, inorganicmaterials, components, substrates, modules, devices, solids, liquids,gases, operating methods, manufacturing methods, or the like aredescribed, part of the diagram or the text is taken out, and oneembodiment of the invention can be constituted. For example, M pieces ofcircuit elements (e.g., transistors or capacitors) (M is an integer,where M<N) are taken out from a circuit diagram in which N pieces ofcircuit elements (e.g., transistors or capacitors) (N is an integer) areprovided, and one embodiment of the invention can be constituted. Asanother example, M pieces of layers (M is an integer, where M<N) aretaken out from a cross-sectional view in which N pieces of layers (N isan integer) are provided, and one embodiment of the invention can beconstituted. As another example, M pieces of elements (If is an integer,where M<N) are taken out from a flow chart in which N pieces of elements(N is an integer) are provided, and one embodiment of the invention canbe constituted.

(Embodiment 1)

Super-resolution processing is processing for generating high-resolutionimages from low-resolution images. Alternatively, super-resolutionprocessing is processing for restoring lost data in photographing,signal transmitting, or the like. Therefore, by performingsuper-resolution processing on averaged images whose detailed parts arecrushed due to low resolution, images whose detailed parts can beaccurately recognized can be generated. Thus, in the case of displayingsuch high-resolution images, high-quality images can be displayed. Forexample, in the case of an image of a park where a great number of smallstones are disposed or a tree having a great number of small leaves, byperforming super-resolution processing, an image of each small stone oreach small leaf can be accurately recognized. In a similar manner, byperforming super-resolution processing, detailed parts of a characterwhich cannot be read due to blur can be recognized. Thus, the charactercan be accurately read. That is, the character can be read as if aperson viewing the character recovered his/her eyesight. For example, insuper-resolution processing, an image having a resolution (the number ofpixels) of 1920×1080 is generated from an image having a resolution (thenumber of pixels) of 1440×1080 by restoration of image data. That is, itcan be said that a super-resolution processing technology is atechnology by which the amount of image data is increased from theamount of image data of an original image and resolution conversion isperformed. Alternatively, it can be said that a super-resolutionprocessing technology is a technology by which the resolution of animage in a format is not changed but the substantial resolution of theimage is increased. Alternatively, it can be said that asuper-resolution processing technology is a technology by which afrequency component which is higher than Nyquist frequency determined bystandard frequency of an input image is restored in data contained in animage.

In display devices such as television sets, display of images which areperceived as clear images by a person viewing the images is emphasizedmore than display of original images precisely in some cases. Forexample, in the case where three-dimensional real world is photographedwith a two-dimensional imaging device, depth data is lost. Therefore, inthe case where the photographed images are displayed precisely, it isdifficult to express stereoscopic effects and reality. Thus, a varietyof image processings are performed on the original images. An example ofsuch image processing is edge enhancement processing. By displaying anedge portion of an object emphatically, the object can be displayedclearly and stereoscopic effects and reality can be expressed.

Thus, by performing both edge enhancement processing andsuper-resolution processing, a realistic image whose detailed parts canbe recognized can be displayed. If super-resolution processing is notperformed but edge enhancement processing is performed, an image isdisplayed in a blurred state, though an edge of the image can be seenclearly. On the other hand, if edge enhancement processing is notperformed but super-resolution processing is performed, an edge of animage is blurred and the image has little reality, though the imagewhose detailed parts can be recognized can be displayed. Accordingly, inorder to display a realistic image whose detailed parts can berecognized, it is preferable to perform both edge enhancement processingand super-resolution processing. Note that one example of thisembodiment is not limited to this.

Note that as for image processing such as edge enhancement processing,one example of this embodiment is not limited to the above example.Different image processing can be performed. As different imageprocessing, for example, smoothing, distortion correction, errorprocessing, flaw correction, color correction, gamma correction, inversegamma correction, or the like can be performed instead of or in additionto the edge enhancement processing. For example, by color correction, animage with 100% or less NTSC ratio can be converted into an image with100% or more NTSC ratio. Thus, an image having high color purity can bedisplayed.

Note that a plurality of image processings such as edge enhancementprocessing can be performed. In that case, the processings can beperformed successively. However, one example of this embodiment is notlimited to this. The plurality of processings can be performedseparately. For example, certain image processing can be performedbefore processing A and different image processing can be performedafter processing B.

Thus, FIGS. 1A and 1B illustrate examples of processing flows in thecase where edge enhancement processing and super-resolution processingare performed. Note that an image can be displayed by performing avariety of processings before and after super-resolution processing orbefore and after edge enhancement processing.

FIG. 1A illustrates a processing flow in the case where super-resolutionprocessing is performed so that resolution is increased after edgeenhancement processing is performed using an image signal obtained froman image source. A variety of processings are further performed afterthe super-resolution processing is performed. After that, an image canbe displayed.

In FIG. 1B, image analysis is performed using an image signal obtainedfrom an image source before super-resolution processing or edgeenhancement processing is performed. Then, a region on whichsuper-resolution processing is to be performed and a region on whichedge enhancement processing is to be performed are recognized. Afterthat, super-resolution processing is performed on the region on whichsuper-resolution processing should be performed and edge enhancementprocessing is performed on the region on which edge enhancementprocessing should be performed. Finally, processing results of the bothprocessings are gathered. That is, the super-resolution processing andthe edge enhancement processing are concurrently performed on one image,though the processings are performed on different regions. In this case,on an edge portion, the super-resolution processing is not performed butthe edge enhancement processing is performed. In a similar manner, theedge enhancement processing is not performed on a portion on which thesuper-resolution processing is performed. Note that one example of thisembodiment is not limited to this.

Note that in image analysis processing, for example, the whole portionof one image is divided into an edge portion, a flat portion, a textureportion, and the like. Edge enhancement processing is performed on theedge portion. Super-resolution processing is performed on the textureportion. Note that one example of this embodiment is not limited tothis.

Here, the flat portion is a portion where regions having specificfrequency or regions having specific luminance are highly distributed.Thus, a sky whose color distribution is comparatively gradual, a dimbackground, or the like corresponds to the flat portion. Therefore, itcan be said that the flat portion is a region whose color is mainlyexpressed gradationally in an image.

Here, the textual portion is a high-frequency portion of an image. Sincethis region has high frequency, it is highly possible that a moredetailed portion exist. Therefore, by performing the super-resolutionprocessing on the textural portion, it can be said that the increase inresolution is highly effective.

Note that as the image analysis processing, instead of or in addition tothe processing of dividing the whole portion of one image into an edgeportion, a flat portion, a texture portion, and the like, processing foranalyzing the resolution of an image can be performed. For example, inthe case of performing super-resolution processing, resolution of avariety of regions of the image is recognized and super-resolutionprocessing can be performed on each region at different intensity.Therefore, as the image analysis processing, instead of or in additionto processing for analyzing whether edge enhancement processing orsuper-resolution processing is performed, processing for analyzing theresolution of an image can be performed.

Note that the image source includes a signal of TV broadcast, which istransmitted from a broadcast station, and/or an image generated from thesignal. Alternatively, the image source includes a signal obtained froman optical storage medium (including a magnetic storage medium or amagnetooptical storage medium) such as a DVD (including a Blu-ray DVD orthe like) or a CD, streaming, the Internet, or the like; and/or an imagegenerated from the signal. Alternatively, the image source includes asignal obtained from a mobile phone, a computer, a CPU, a graphicmicrocomputer, a controller, an electronic device, or the like; and/oran image generated from the signal. Alternatively, the image sourceincludes a signal used for performing display and/or an image generatedfrom the signal.

Note that the image includes a still image and/or a moving image and/ora screen image.

Note that the image source can be an interlace image or a progressive(non-interlace) image. Alternatively, the image source can be an imageon which IP conversion (interlace-progressive conversion), which isprocessing for converting interlace images into progressive images, hasalready been performed. Alternatively. IP conversion can be performedbefore and after edge enhancement processing is performed or beforesuper-resolution processing is performed. FIG. 2A illustrates part of aprocessing flow in the case where super-resolution processing isperformed on a progressive image. FIG. 2B illustrates part of aprocessing flow in the case where edge enhancement processing isperformed after IP conversion is performed on an interlace image. FIG.2C illustrates part of a processing flow in the case where edgeenhancement processing is performed after IP conversion is performed onan interlace image, and then super-resolution processing is performed.FIG. 2D illustrates part of a processing flow in the case wheresuper-resolution processing is performed after IP conversion isperformed on an interlace image.

Usually, super-resolution processing is performed on one image (or partof the image) or a plurality of images (or parts of the images). Inaddition, in the super-resolution processing, new data is generatedusing such an image so that a high-resolution image is generated.Therefore, in order to accurately perform the super-resolutionprocessing, it is not preferable that part of image data be lost as inan interlace image. Accordingly, it is preferable that an image on whichthe super-resolution processing be performed be a progressive(non-interlace) image. Thus, in the case of an interlace image, it ispreferable that IP conversion be performed before the super-resolutionprocessing is performed and the super-resolution processing be performedon a progressive image. Note that one example of this embodiment is notlimited to this.

Note that IP conversion can be performed before or aftersuper-resolution processing. Alternatively, IP conversion can beperformed before or after edge enhancement processing. Alternatively, IPconversion can be performed before or after different processing.

Note that as illustrated in FIG. 3A, for example, it is preferable thatthe resolution (the number of pixels) of an image subjected tosuper-resolution processing be higher than the resolution (the number ofpixels) of an image before subjected to the super-resolution processing.However, one example of this embodiment is not limited to this. Forexample, before the super-resolution processing is performed, resolution(the number of pixels) has already been high by enlargement processingor the like. That is, resolution (the number of pixels) of the image ina format is made high. In that case, since the resolution has alreadybeen high, the resolution itself is not changed before and after thesuper-resolution processing. That is, the resolution (the number ofpixels) of the image in the format is not changed. However, inenlargement processing before the super-resolution processing, missingimage data is not restored. That is, the image is just enlarged anddisplay itself does not have high quality. The resolution (the number ofpixels) of the image in the format is just made high and substantialresolution is not made high. For example, in the case of an image of apark where a great number of small stones are disposed or a tree havinga great number of small leaves, an image of each small stone or eachsmall leaf is not accurately displayed by enlargement processing but isjust enlarged in a blurred state. Thus, by performing thesuper-resolution processing, it is possible to restore missing imagedata and to generate a high-quality image whose detailed parts can berecognized, though the resolution (the number of pixels) of an image isnot changed. That is, it is possible not to change the resolution of theimage in the format but to make the substantial resolution high. Inother words, as illustrated in FIG. 3B, it is possible to generate animage having a resolution of 1920×1080 from an image having a resolutionof 1440×1080 by enlargement processing and to generate an image having aresolution of 1920×1080 from the image having a resolution of 1920×1080by super-resolution processing. In this case, in the case where theimage having a resolution of 1920×1080 is generated from the imagehaving a resolution of 1440×1080 by the enlargement processing, there isno restored data. However, after the super-resolution processing isperformed, data is restored. Thus, an image whose detailed parts can beaccurately recognized can be generated.

Note that such processing is performed on the entire screen in manycases; however, one example of this embodiment is not limited to this.Such processing can be performed on part of the screen.

Note that it is possible to make resolution high by enlargementprocessing and then to make the resolution higher by super-resolutionprocessing. That is, it is possible to make substantial resolution highby super-resolution processing after resolution in a format is made highby enlargement processing. For example, it is possible to generate animage having a resolution of 1440×1080 from an image having a resolutionof 800×600 by enlargement processing and to generate an image having aresolution of 1920×1080 from the image having a resolution of 1440×1080by super-resolution processing. Note that in the case of making theresolution high by the enlargement processing, data is not restored. Onthe other hand, in the case of making the resolution high by thesuper-resolution processing, data is restored. Note that one example ofthis embodiment is not limited to this.

Alternatively, it is possible to make resolution high bysuper-resolution processing and then to make the resolution higher byenlargement processing. That is, it is possible to make resolution in aformat high by enlargement processing after substantial resolution ismade high by super-resolution processing. For example, it is possible togenerate an image having a resolution of 1440×1080 from an image havinga resolution of 800×600 by super-resolution processing and to generatean image having a resolution of 1920×1080 from the image having aresolution of 1440×1080 by enlargement processing. Note that in the caseof making the resolution high by the enlargement processing, data is notrestored. On the other hand, in the case of making the resolution highby the super-resolution processing, data is restored. Note that oneexample of this embodiment is not limited to this.

Note that enlargement processing can be performed before or aftersuper-resolution processing. Alternatively, enlargement processing canbe performed before or after edge enhancement processing. Alternatively,enlargement processing can be performed before or after differentprocessing. Note that one example of this embodiment is not limited tothis.

Both enlargement processing and super-resolution processing can beperformed in this manner. For example, in the case where longitudinal orlateral resolution is made twice or more, preferably five times or more,it is preferable to perform both enlargement processing andsuper-resolution processing. Note that one example of this embodiment isnot limited to this.

Note that as the enlargement processing, for example, bi-linearinterpolation, bi-cubic convolution, or the like can be used. Bi-linearinterpolation is a method by which four surrounding pixels are extractedand calculated and insufficient images are interpolated in enlargement.In bi-cubic convolution, 16 pixel values (4×4 pixel values) in standardsof coordinate after conversion are extracted from a coordinate beforethe conversion. Then, weighted-average calculation is performed byweighting of the extracted 16 pixel values so that the pixel valuesafter the conversion are determined. Alternatively, a variety ofenlargement processings can be used.

Note that as illustrated in FIG. 3C, whether enlargement processing isperformed on an image is analyzed. In the case where enlargementprocessing is performed on part or all of a screen, super-resolutionprocessing is performed. In the case where enlargement processing is notperformed, i.e., in the case where resolution is originally high,super-resolution processing can be omitted. Since a variety of imagesare used as image sources, by performing image analysis,super-resolution processing can be accurately performed even on an imageon which enlargement processing is performed. Note that as an example ofan image analysis method, there is a method by which frequency analysisis performed and whether frequency is high is determined. In the casewhere frequency is low, it can be determined that enlargement processinghas been performed.

Note that the image analysis in FIG. 3C, the image analysis in FIG. 1B,and/or the image resolution analysis in FIG. 1B can be performedcollectively. Alternatively, the image analysis in FIG. 3C, the imageanalysis in FIG. 1B, and/or the image resolution analysis in FIG. 1B canbe performed concurrently. Alternatively, the image analysis in FIG. 3C,the image analysis in FIG. 1B, and/or the image resolution analysis inFIG. 1B can be performed successively. Note that one example of thisembodiment is not limited to this.

Note that in FIG. 3B, FIG. 3C, or the like, different processing can beperformed before and after enlargement processing. For example, FIG. 3Dillustrates an example of the case where edge enhancement processing isperformed after enlargement processing in FIG. 3B.

Note that as in FIG. 1B, super-resolution processing and differentprocessing such as edge enhancement processing can be performedconcurrently in FIG. 3A, FIG. 3B, FIG. 3C, or the like.

Note that in the contents described thus far and/or contents describedbelow, simple enlargement processing or the like can be performedinstead of super-resolution processing.

Note that the content or the drawing described in this embodiment can beapplied to the case where different processing is performed in a similarmanner. In a similar manner, the content or the drawing described incertain processing can be applied to the case where different processingis performed.

(Embodiment 2)

Next, examples of super-resolution processing technologies aredescribed. By performing super-resolution processing, a high-resolutionimage can be displayed.

First, a moving region is detected and speed data of the region isextracted. That is, with respect to an image at given time, an opticalflow, which is a vector illustrating the flow of each pixel, iscalculated from two images before and after the image. Then, from theextracted speed data, the amount of positional deviation per image inthe region is detected with accuracy of less than the size of one pixel.That is, from the calculated optical flow, the amount of positionaldeviation between images is calculated. Then, in accordance with theamount of detected positional deviation, the level of luminance betweenpixels is interpolated from a plurality of images in an image column.With such processing, a high-resolution image having resolution which ishigher than physical resolution can be generated. Thus, it can be saidthat the super-resolution processing technology is a technology by whichdata for restoring a high-resolution image is extracted and restoredfrom a low-resolution image in accordance with motion vector data or thelike.

In a similar super-resolution processing technology, for example, first,consecutive frames having close correlation are selected from images.After that, the motion vector of the images are detected with finenesswhich is close to the size of one pixel. Then, the motion of each pixelis tracked, and a missing high-resolution pixel is estimated from datarelated to a change in the tracked pixel between respective frames. Inthis case, since a camera slightly swings, crushing of a photographedlow-resolution portion is varied between the frames, though the sameportion is photographed. Thus, with this data, the missing pixel can becompensated and high resolution can be realized. That is, it can be saidthat this processing method is a super-resolution technology by whichsearch is performed sufficiently in a time direction. In the case ofthis super-resolution technology, motion vectors can be recognizedprecisely. Thus, a missing pixel between frames, which cannot beacquired in photographing due to the resolution of a camera, can also berestored.

Alternatively, in different super-resolution processing, the similarityof a plurality of frames is found out. After that, the frames havingsimilarity are aligned, and a time change in each pixel is recognized.Then, a method by which a missing high-resolution pixel is estimated andgenerated can be used.

Alternatively, in different super-resolution processing, first, datarelated to a consecutive plurality of images is analyzed. Then, ahigh-frequency component is restored by correction of common portions ofphotographic objects. Thus, a high-resolution image can be obtained.

Alternatively, as different super-resolution processing, areconstruction super-resolution processing method can be used. In thereconstruction super-resolution processing method, first,high-resolution images (initial high-resolution images) are assumed fromoriginal low-resolution images. Then, in accordance with a point spreadfunction (PSF) obtained from the model of a camera, the pixel values ofall the pixels of the low-resolution images are estimated from theassumed high-resolution images. In other words, the assumedhigh-resolution images are down-converted by a unique function (animaging model function) so that low-resolution images having the sameresolution as the original low-resolution images are generated. Then, adifference between the estimated value and an observed pixel value (anobserved value) is calculated. After that, with respect to the imagesbefore subjected to down conversion, high-resolution images in which theabove difference is smaller are searched. Note that this searchprocessing can be repeated until convergence so that accuracy is madehigh, or can be performed only once. Thus, high-resolution images can beobtained.

Note that as the imaging model function, for example, an imaging elementmodel where processing is performed two-dimensionally (lengthwise andwidthwise) by using a one-dimensional linear filter can be used.

In the case of this reconstruction super-resolution processing method,high-resolution images are reconstructed by iterative calculation whichneeds initial high-resolution images. As a calculation method in thatcase, an ML (maximum-likelihood) method, a MAP (maximum a posterior)method, a POCS (projection on to convex sets) method, or the like can beused.

In the ML method, a square error between an estimated pixel value of anassumed high-resolution image and a pixel value which is actuallyobserved is used as an evaluation function. In the ML method, ahigh-resolution image in which the evaluation function is minimized isused as an estimated image.

The MAP method is a method by which a high-resolution image in which anevaluation function where the probability information of ahigh-resolution image is added to a square error is minimized isestimated. In other words, the MAP method is a super-resolutionprocessing method by which a high-resolution image is estimated as anoptimization problem for maximizing posterior probability by utilizingforeseeing data related to a high-resolution image.

The POCS method is a method by which a simultaneous equation of pixelvalues of a high-resolution image and a low-resolution image is formedand sequentially solved.

Note that one frame is formed by merging a plurality of frames of animage. Thus, the image is made to have higher resolution by the increasein the number of pixels. In this case, processing for making resolutionhigher can be performed such that a return component is canceled.

Alternatively, as a super-resolution processing method, an iterationmethod, a frequency-domain method, a statistical method, or the like canbe used. The iteration method mainly includes three steps: a first stepof initial estimation, a second step of imaging, and a third step ofreconstructing.

Note that super-resolution processing can be performed on the wholescreen. However, one example of this embodiment is not limited to this.The super-resolution processing can be performed depending on thecontent of an image. For example, the super-resolution processing is notperformed on an edge portion or a flat portion of an image but thesuper-resolution processing can be performed on a textual portion of theimage. In that case, real-time spectrum analysis is performed on theimage. In addition, the super-resolution processing can be performed ononly a high-frequency region. By controlling whether thesuper-resolution processing is performed or not depending on an image,the image can be prevented from deteriorating.

Note that the flat portion is a portion where regions having specificfrequency or regions having specific luminance are highly distributed.Thus, a sky whose color distribution is comparatively gradual, a dimbackground, or the like corresponds to the flat portion. Therefore, itcan be said that the flat portion is a region whose color is mainlyexpressed gradationally in an image.

Note that the textual portion is a high-frequency portion of an image.Since this region has high frequency, it is highly possible that a moredetailed portion exist. Therefore, by performing the super-resolutionprocessing on the textural portion, it can be said that the increase inresolution is highly effective.

Note that in the case of performing super-resolution processing,resolution of a variety of regions of an image is recognized andsuper-resolution processing can be performed on each region at differentintensity.

Note that if the resolution of an original image is sufficiently high,super-resolution processing can be omitted. After determining whetherthe resolution of the original image is high, whether super-resolutionprocessing is performed can be controlled depending on the result.

Although a variety of super-resolution processing technologies have beendescribed above, the super-resolution processing technology in thisspecification is not limited to them.

(Embodiment 3)

Note that an image can be displayed by performing a variety ofprocessings before and after super-resolution processing or before andafter edge enhancement processing. Therefore, the content described inany of the other embodiments can be applied to, combined with, orreplaced with this embodiment.

In hold-type displays such as liquid crystal display devices, in thecase where fast-moving images are displayed, motion blur occurs andafterimages are seen in some cases. For example, in the case where acharacter is displayed in a ticker and is moved up and down or right andleft, the character is blurred and cannot be accurately recognized insome cases.

Therefore, by performing frame interpolation processing, frame frequencycan be improved and the resolution of moving images can be improved. Theframe interpolation processing is processing by which frame data isinterpolated when display is performed at higher frame frequency inorder to reduce afterimages or the like. For example, as illustrated inFIG. 4A, a circle is displayed on the left in an image of a first frame,and the circle is moved from left to right in an image of a second frameand is displayed on the right. In this case, data where a circle isdisplayed in the center is generated. Processing by which data isgenerated in this manner is the frame interpolation processing. Inaddition, by the frame interpolation processing, frame frequency indisplay can be made high by the number of interpolated frames. Byperforming display with frame frequency made high by frame interpolationprocessing in this manner, a smooth image where a circle is moved fromleft to right can be displayed and afterimages can be reduced.Therefore, since moving images can be displayed without blur, theresolution of the moving images can be improved.

Driving by which frame interpolation is performed and frame frequency ismade high to a corresponding extent in this manner is referred to asframe rate doubling. For example, when frame frequency is double, suchdriving is referred to as double-frame rate driving. When framefrequency is quadruple, such driving is referred to as quadruple-framerate driving. In the case of the double-frame rate driving, images offrames whose number is the same as the number of original frames aregenerated by frame interpolation processing. Accordingly, the totalamount of data is double, so that images can be displayed at doubleframe frequency. In a similar manner, in the case of the quadruple-framerate driving, images of frames whose number is three times as large asthe number of original frames are generated by frame interpolationprocessing. Accordingly, the total amount of data is quadruple, so thatimages can be displayed at quadruple frame frequency. By performing suchframe rate doubling, moving-image characteristics can be improved andafterimages can be reduced. As a display device to which frame ratedoubling is applied, a hold-type display device is preferable. Forexample, the frame rate doubling is preferably applied to a liquidcrystal display, an organic EL display, or the like. Since afterimagesare easily visible in hold-type display devices, afterimages can bereduced by frame rate doubling.

Thus, by performing both frame interpolation processing andsuper-resolution processing, the resolution of still images and theresolution of moving images can be improved. If neither frameinterpolation processing nor frame rate doubling is performed but onlysuper-resolution processing is performed, images are blurred due toafterimages or the like, though the resolution of the images is madehigh by the super-resolution processing. Thus, the higher resolutioncannot be easily perceived. That is, an advantageous effect of thesuper-resolution processing is reduced. Alternatively, ifsuper-resolution processing is not performed but only frameinterpolation processing and frame rate doubling are performed, theresolution of images to be displayed itself is low, though the movingimages can be accurately perceived. Therefore, high-quality imagescannot be displayed. Accordingly, regardless of still images or movingimages, it is preferable to perform both frame interpolation processingand super-resolution processing in order to display high-resolutionimages accurately. Note that one example of this embodiment is notlimited to this.

Thus, FIG. 5A illustrates a processing flow in the case where edgeenhancement processing is performed, frame interpolation is performed,and then super-resolution processing is performed. FIG. 5B illustrates aprocessing flow in the case where frame interpolation is performed, edgeenhancement processing is performed, and then super-resolutionprocessing is performed. FIG. 5C illustrates a processing flow in thecase where frame interpolation is performed, image analysis isperformed, and super-resolution processing and edge enhancementprocessing are performed. Note that it is possible to perform imageanalysis, to perform frame interpolation processing, and then to performsuper-resolution processing and edge enhancement processing. Afterprocessings as in each of FIGS. 5A to 5C, a variety of processings areperformed, and then, an image can be displayed. The processing flow inFIG. 5A or FIG. 5B corresponds to a processing flow where frameinterpolation processing is added to the processing flow in FIG. 1A. Ina similar manner, the processing flow in FIG. 5C corresponds to aprocessing flow where frame interpolation processing is added to theprocessing flow in FIG. 1B.

Note that before and after each stage in the processing flow, a varietyof different processings can be performed. As examples of a variety ofdifferent processings, there are IP conversion processing, enlargementprocessing, and the like. Further, different processing is possible.

Note that by performing the frame interpolation processing after theedge enhancement processing is performed as illustrated in FIG. 5A, thenumber of edge enhancement processings can be reduced. The number offrames is small before the frame interpolation processing is performed.Therefore, before the frame interpolation processing is performed, thenumber of frames on which the edge enhancement processing is performedis also small. Thus, the number of processings can be reduced.

Note that by performing the frame interpolation processing before theedge enhancement processing is performed as illustrated in FIG. 5B orFIG. 5C, data for frame interpolation can be accurately generated. Sincethe edge enhancement processing can be performed on a more accuratehigh-resolution image, the edge of an object in the image can be moreaccurately acquired. Thus, a clearer image can be obtained.

By performing frame interpolation processing after edge enhancementprocessing is performed in this manner, the frame interpolationprocessing can be performed more accurately. Through the edgeenhancement processing, part of an image is changed. Therefore, byperforming the frame interpolation processing using data before change,the processing can be performed accurately.

Next, it is assumed that by performing super-resolution processing on animage having lateral resolution (the number of pixels) of A andlongitudinal resolution (the number of pixels) of B, the image ischanged into an image having lateral resolution (the number of pixels)of C and longitudinal resolution (the number of pixels) of D.Alternatively, it is assumed that by performing enlargement processingand the super-resolution processing on an image having the lateralresolution (the number of pixels) of A and the longitudinal resolution(the number of pixels) of B, the image is changed into an image havingthe lateral resolution (the number of pixels) of C and the longitudinalresolution (the number of pixels) of D. In this case, it can be saidthat a multiplying factor when the resolution is made high by thesuper-resolution processing is C/A, where C is divided by A, or D/B,where D is divided by B. In addition, it is assumed that in the case ofperforming frame rate doubling, frame frequency is N times.

Note that here, each of A, B, C, and D, which represents resolution, ispreferably resolution of an image in a format or substantial resolution.Note that one example of this embodiment is not limited to this.

In this case, N>(C/A) or N>(D/B) is preferable. Alternatively, N≥(C/A)and N≥(D/B) are preferable. Note that one example of this embodiment isnot limited to this. Note that here, each of A, B, C, D, and N is anatural number.

In the case of performing frame interpolation processing for frame ratedoubling, even when the amount of frame data to be interpolated is madelarge, data can be generated without problems. For example, FIG. 4Aillustrates double-frame rate driving; however, by adjustment of theposition of a circle as illustrated in FIG. 4B, triple-frame ratedriving can be easily realized. That is, in the frame interpolationprocessing for the frame rate doubling, even when the amount of framedata to be interpolated is made large, big problems do not occur in animage. Alternatively, by making the amount of frame data to beinterpolated large, moving-image characteristics can be further improvedand afterimages can be further reduced.

On the other hand, the super-resolution processing is processing bywhich resolution data which is lost in photographing or signaltransmitting is restored. Therefore, if a large amount of data is lost,it is difficult to restore the data adequately. Accordingly, when thevalue of (C/A) or (D/B) is too large, problems occur in an image itselfand the image is distorted.

From the above, when both frame interpolation processing andsuper-resolution processing are performed, N>(C/A) or N>(D/B) ispreferable. Alternatively, N≥(C/A) and N≥(D/B) are preferable. Thus,when both the frame interpolation processing and the super-resolutionprocessing are performed and the above relationship is satisfied, ahigh-quality image in which detailed parts are clear and afterimagefeeling is eliminated can be displayed. Note that one example of thisembodiment is not limited to this.

Note that in the case of performing frame interpolation processing, in amoving region of a screen, data is additionally generated for the frameinterpolation processing in many cases. In addition, in a static regionof the screen, data is not additionally generated in many cases. Thatis, in the screen, there are a region where data is additionallygenerated by frame interpolation processing and a region where data isnot additionally generated. For example, in the case of FIG. 4A, in aregion 301 and a region 303, data of the first frame before subjected tointerpolation and data of the second frame before subjected to theinterpolation do not change, as illustrated in FIG. 4C. Therefore, thereis no change even in frame data to be interpolated and data is notadditionally generated. Data is generated by utilizing the data of thefirst frame before subjected to the interpolation or the data of thesecond frame before subjected to the interpolation. On the other hand,in a region 302, data of the first frame before subjected to theinterpolation and data of the second frame before subjected to theinterpolation change, so that there are a region where the circle iserased and a region where the circle is generated. Thus, data isadditionally generated.

In the case of performing frame interpolation processing in this manner,in a screen, there are a region where data is additionally generated anda region where data is not additionally generated. In addition, suchregions change over time. For example, as an example of a region wheredata is generated, a region can be given in which a character isdisplayed in a ticker or the like and is moved up and down or right andleft. In the case of a character, a symbol, or the like, whenafterimages are generated and the character, the symbol, or the like isnot easily seen, it is impossible to determine the type of thecharacter, the symbol, or the like, which is a big problem.

Generation of additional data only in parts of regions in a screen whenframe interpolation processing is performed in this manner hasadvantages such as improvement in processing speed, reduction in powerconsumption, and improvement in processing accuracy.

Further, super-resolution processing can be performed not on all regionsin a screen but on parts of the regions in the screen. For example, inthe case where a streaming broadcast is displayed on part of a screen, alow-resolution image is displayed on only in that region while beingenlarged in some cases. In such a case, by performing super-resolutionprocessing on only the region where the streaming broadcast isdisplayed, image quality can be improved.

In the case of performing super-resolution processing only on parts ofregions in a screen in this manner, there is an advantage such asimprovement in processing speed, reduction in power consumption,improvement in processing accuracy, or reduction in image defects.

Therefore, in a screen, there are a first region where data isadditionally generated for frame interpolation processing and a secondregion where super-resolution processing is performed. Further, a thirdregion where data is not additionally generated for frame interpolationprocessing and super-resolution processing is not performed can beprovided. Furthermore, a region where the first region and the secondregion do not overlap with each other can be provided in the screen.Alternatively, a region where the first region and the second regionoverlap with each other can be provided in the screen.

Data is additionally generated for frame interpolation processing in aregion where data related to a character or a symbol, such as a tickerin many cases. Super-resolution processing is performed on a region withlittle motion in many cases. Therefore, in the screen, it is preferablethat the region be provided in which the first region where data isadditionally generated for the frame interpolation processing does notoverlap with the second region where the super-resolution processing isperformed. The reason for this is as follows. Since the first regionwhere data is additionally generated for the frame interpolationprocessing is a moving region, data is additionally generated for theframe interpolation processing in order to make afterimages invisible.However, in such a moving region, even if resolution is made high bysuper-resolution processing, it may be difficult for eyes to recognizethe resolution. Therefore, in such a moving region, it can be said thatsuper-resolution processing is not performed in some cases. The secondregion where the super-resolution processing is performed is a regionwhose detailed parts are preferably seen clearly. In the case where astatic image such as a still image is displayed, it can be said thatdetailed parts are seen clearly. Since there is a possibility ofoccurrence of the above condition, a region can be provided in which afirst region where both frame interpolation processing andsuper-resolution processing are performed, the screen can be displayedwith advantages of both of the processings, and data is additionallygenerated for the frame interpolation processing does not overlap withthe second region where the super-resolution processing is performed.Accordingly, a more appropriate image can be displayed. Note that oneexample of this embodiment is not limited to this.

By performing both frame interpolation processing and super-resolutionprocessing in this manner, images having high image picture resolutionand high moving image resolution can be displayed.

Note that in the case where super-resolution processing is performedafter frame interpolation processing is performed, frame frequency ismade high for the frame interpolation processing. Therefore, processingspeed of the super-resolution processing is not sufficiently high insome cases. Thus, a plurality of processing systems for thesuper-resolution processing can be provided. For example, FIGS. 6A and6B each illustrate the case where two processing systems for thesuper-resolution processing are provided. FIG. 6A illustrates the casewhere two processing systems for the super-resolution processing areprovided in FIG. 5A. FIG. 6B illustrates the case where two processingsystems for the super-resolution processing are provided in FIG. 5B. Asin FIGS. 6A and 6B, the number of processing systems can be optimal.

In the case where a plurality of processing systems are provided,processings can be divided among the processing systems by a variety ofmethods. For example, processing for a right half of a screen can beperformed by a first super-resolution processing system, and processingfor a left half of the screen can be performed by a secondsuper-resolution processing system. Since image data related to an imageis usually transferred in each row, processings can be divided betweenthe first super-resolution processing system and the secondsuper-resolution processing system by division of image data for one rowinto two pieces of data for the right half and left half of the screen.Note that one example of this embodiment is not limited to this.

Alternatively, processing of a certain frame (e.g., an odd-numberedframe or a frame on which frame interpolation processing is notperformed) can be performed by the first super-resolution processingsystem, and processing of a different frame (e.g., an even-numberedframe or a frame generated by frame interpolation processing) can beperformed by the second super-resolution processing system. Thus, evenwhen the processing speed of the super-resolution processing is lowerthan the frame frequency, processing can be completed normally byalternate processings. Alternatively, since the processing speed of oneprocessing system may be low, power consumption can be reduced.

Note that one example of this embodiment is not limited to the casewhere super-resolution processing is performed after frame interpolationprocessing is performed. For example, as illustrated in FIG. 7A,super-resolution processing can be performed while performing frameinterpolation processing. First, image data A is supplied from an imagesource. Then, image processing such as edge enhancement processing isperformed. The image data A is not image data generated by the frameinterpolation processing. Therefore, the super-resolution processing canbe performed immediately. Next, image data B is supplied from the imagesource. Then, image processing such as edge enhancement processing isperformed. After that, frame data is interpolated using the image data Aand the image data B which have already been supplied. When the frameinterpolation processing is performed using the image data A and theimage data B, the super-resolution processing can be performed using theimage data A. That is, the image data A is used for both of the frameinterpolation processing and the super-resolution processing. Thus, thesuper-resolution processing and the frame interpolation processing canbe performed concurrently. After that, by the frame interpolationprocessing with the use of the image data A and the image data B, imagedata C is generated. Then, super-resolution processing is performed onthe image data C obtained by the frame interpolation with the use of theimage data A and the image data B. By concurrently performing the frameinterpolation processing and the super-resolution processing in thismanner, the number of memories for storing the image data A can bereduced. When the image data A is stored in one memory, thesuper-resolution processing and the frame interpolation processing canbe performed by reading of the data. Note that as for image data whereframe data is generated, it can be said that the super-resolutionprocessing is performed after the frame interpolation processing isperformed. Note that one example of this embodiment is not limited tothis.

Note that as in FIG. 6A, a plurality of processing systems can beprovided for super-resolution processing, and the super-resolutionprocessing and frame interpolation processing can be performedconcurrently. FIG. 7B illustrates an example of such a case. Forexample, after edge enhancement processing is performed,super-resolution processing is performed on at least the image data A byusing the second super-resolution processing system. Concurrently, theframe interpolation processing is performed using at least the imagedata A. That is, the frame interpolation processing and thesuper-resolution processing are concurrently performed using at leastthe image data A. After that, the super-resolution processing isperformed on image data on which frame interpolation is performed usingthe first super-resolution processing system. By providing a pluralityof super-resolution processing systems in this manner, processings canbe performed concurrently. Further, the super-resolution processing canbe performed quickly on frame data which is not generated by the frameinterpolation with the use of the second super-resolution processingsystem. Therefore, when image data is input, the image can be displayedquickly. Accordingly, such processing is preferable in the case ofdisplaying an image of a game or the like, where real-time processing isneeded. Note that one example of this embodiment is not limited to this.

Note that in the case where a plurality of processings are performedconcurrently, the processings can be performed concurrently only in partof the processing period of each processing. In other words, even in thecase where a plurality of processings are performed concurrently, aperiod during which the plurality of processings are not performedconcurrently can be provided. Alternatively, the plurality ofprocessings can be performed concurrently in all the processing periodof each processing.

Alternatively, processing may be performed as illustrated in FIG. 7C.For example, after edge enhancement processing is performed,super-resolution processing is performed on at least the image data A byusing the first super-resolution processing system or the secondsuper-resolution processing system. Concurrently, the frameinterpolation processing is performed using at least the image data A.That is, the frame interpolation processing and the super-resolutionprocessing are concurrently performed using at least the image data A.After that, the super-resolution processing is performed on image dataon which frame interpolation is performed using the secondsuper-resolution processing system or the first super-resolutionprocessing system. By providing a plurality of super-resolutionprocessing systems in this manner, processings can be performedconcurrently. Further, the super-resolution processing can be performedquickly on frame data which is not generated by the frame interpolationwith the use of the first super-resolution processing system or thesecond super-resolution processing system. Therefore, when image data isinput, the image can be displayed quickly. Accordingly, such processingis preferable in the case of displaying an image of a game or the like,where real-time processing is needed. Note that one example of thisembodiment is not limited to this.

Note that FIGS. 1A and 1B, FIGS. 2A to 2D, FIGS. 3A to 3D, FIGS. 4A to4C, FIGS. 5A to 5C, FIGS. 6A and 6B, and FIGS. 7A to 7C illustrate theprocessing flows as examples, and FIG. 8A illustrates an example of astructure (a block diagram) for realizing the processing flows. Forexample, an image source is input to an input terminal of a circuit 101.An output terminal of the circuit 101 is connected to an input terminalof the circuit 102. For example, the circuit 101 has a function ofperforming frame interpolation processing or edge enhancementprocessing. For example, the circuit 102 has a function of performingsuper-resolution processing. The circuit 101 or the circuit 102 caninclude a memory circuit (a memory) for storing data. Alternatively, thecircuit 101 or the circuit 102 can include a unit for calculation.

FIG. 8B illustrates another example of a structure (a block diagram) forrealizing the processing flows. FIG. 8B corresponds to FIG. 1B, FIG. 6A,or FIG. 6B, for example. For example, an image source is input to theinput terminal of the circuit 101. The output terminal of the circuit101 is connected to an input terminal of a circuit 102 a through aswitch 103 a. Further, the output terminal of the circuit 101 isconnected to an input terminal of a circuit 102 b through a switch 103b. An output terminal of the circuit 102 a is connected to an outputterminal through a switch 104 a. Further, an output terminal of thecircuit 102 b is connected to the output terminal through a switch 104b. Note that as illustrated in FIG. 8C, the switch 103 b can beconnected between the input terminal of the circuit 102 b and the inputterminal of the circuit 101. Note that FIG. 8C corresponds to FIG. 7B,for example. The circuit 101 has a function of performing frameinterpolation processing, image analysis processing, or edge enhancementprocessing. Each of the circuit 102 a and the circuit 102 b has afunction of performing super-resolution processing or edge enhancementprocessing. The circuit 101, the circuit 102 a, or the circuit 102 b caninclude a memory circuit (a memory) for storing data. Alternatively, thecircuit 101, the circuit 102 a, or the circuit 102 b can include a unitfor calculation. By controlling the switch 103 a, the switch 103 b, theswitch 104 a, and/or the switch 104 b, processings can be performedconcurrently.

Note that in the circuit 101, the circuit 102, the circuit 102 a, and/orthe circuit 102 b can realize its function with hardware, software, orboth hardware and software. When the circuit 101, the circuit 102, thecircuit 102 a, and/or the circuit 102 b realizes its function withdedicated hardware having a certain function, processing speed can bemade high or power consumption can be reduced. Alternatively, when thecircuit 101, the circuit 102, the circuit 102 a, and/or the circuit 102b realizes its function with software, the content of processing can bechanged and a variety of processings can be performed as appropriate.

Alternatively, by using a multi-core CPU including a plurality of CPUcores and distributing processings across the CPU cores, frameinterpolation processing, edge enhancement processing, a plurality ofsuper-resolution processings, or the like can be performed. With the useof a multi-core CPU in this manner, high-speed operation is possiblewith fewer components. Note that such a multi-core CPU can include asemiconductor device (or a transistor) formed using an SOI. With the useof an SOT, operation can be performed with low power consumption andheat generation during the operation can be suppressed.

Note that even when the number of processings is increased, a circuitcan be formed in a manner similar to those in FIGS. 8A to 8C byincreasing a circuit such as the circuit 101, the circuit 102, thecircuit 102 a, or the circuit 102 b. Note that processing performed inthe circuit 101, the circuit 102, the circuit 102 a, or the circuit 102b is not limited to super-resolution processing, edge enhancementprocessing, frame interpolation processing, or image analysisprocessing. A variety of different processings can be performed.

(Embodiment 4)

An image can be displayed by performing a variety of processings beforeand after a variety of processings such as super-resolution processing.Therefore, the content described in any of the other embodiments can beapplied to, combined with, or replaced with this embodiment.

For example, FIGS. 9A and 9B illustrate processing flows in the casewhere overdrive processing is performed after super-resolutionprocessing. The processing flow in FIG. 9A corresponds to a processingflow where overdrive processing is added to the processing flow in FIG.5A and a processing flow where frame interpolation processing andoverdrive processing are added to the processing flow in FIG. 1A. In asimilar manner, the processing flow in FIG. 9B corresponds to aprocessing flow where overdrive processing is added to the processingflow in FIG. 5B and a processing flow where frame interpolationprocessing and overdrive processing are added to the processing flow inFIG. 1A. Therefore, the contents or the drawings described in theprocessings can be applied to the case where different processing suchas overdrive processing is performed in a similar manner. In a similarmanner, the content or the drawing described in certain processing canbe applied to the case where different processing is performed.

Note that the overdrive processing is processing for making the responsespeed of a liquid crystal element or the like high. Usually, a signalcorresponding to a gray level which is to be expressed in each pixel issupplied to each pixel in a screen. However, since the liquid crystalelement has low response speed, even if a signal corresponding to a graylevel is supplied, display which corresponds to the gray level cannot beperformed in one frame period. After several frame periods, displaywhich corresponds to the gray level is eventually performed. Thus, insupplying voltage to the liquid crystal element, not voltagecorresponding to an original gray level but voltage having largeramplitude is supplied to the liquid crystal element. Accordingly, thetransmittance of the liquid crystal element is drastically changed.After that, voltage corresponding to the original gray level issupplied. Through the above operation, the response speed of the liquidcrystal element can be made high. Driving by which voltage having largeramplitude than voltage corresponding to the original gray level istemporarily supplied to the liquid crystal element before the voltagecorresponding to the original gray level is supplied is referred to asoverdrive. Further, processing for determining which level of voltage issupplied as voltage having larger amplitude than voltage correspondingto the original gray level is referred to as overdrive processing.

By performing overdrive processing after super-resolution processing isperformed, response speed can be made high, the amount of overdrive canbe controlled adequately, and display with fewer afterimages can beperformed. Alternatively, since the super-resolution processing isprocessing by which a new image is generated, an image is changed by theprocessing. Thus, the gray level of each pixel is changed. Therefore, byperforming the overdrive processing after the super-resolutionprocessing is performed, the overdrive processing can be changed inaccordance with the amount of change generated by the super-resolutionprocessing. Accordingly, by performing the overdrive processing afterthe super-resolution processing is performed, the amount of overdrivecan be controlled adequately, so that the gray level of each pixel canbe optimized. Thus, the response speed can be made high and theoverdrive can be accurately performed. Further, by the super-resolutionprocessing, a high-resolution image can be displayed without generationof afterimages. Accordingly, in order to obtain a high-quality image, itis preferable to perform the super-resolution processing before theoverdrive processing is performed. Note that one example of thisembodiment is not limited to this.

Note that here, the amount of overdrive corresponds to an increase involtage supplied to a liquid crystal element or the like, which is anincrease in the amplitude of the voltage by overdrive processing.

In a similar manner, by performing overdrive processing after frameinterpolation processing is performed, response speed can be made high,the amount of overdrive can be controlled adequately, and display withfewer afterimages can be performed. Alternatively, since the frameinterpolation processing is processing for generating new frame data, animage which is changed is generated by the processing. Thus, the graylevel of each pixel is changed. Therefore, by performing the overdriveprocessing after the frame interpolation processing is performed, theoverdrive processing can be changed in accordance with the amount ofchange generated by the frame interpolation processing. Accordingly, byperforming the overdrive processing after the frame interpolationprocessing is performed, the amount of overdrive can be controlledadequately, so that the gray level of each pixel can be optimized. Thus,the response speed can be made high and the overdrive can be accuratelyperformed. Further, by the frame interpolation processing, display withfewer afterimages can be performed. Accordingly, in order to obtain ahigh-quality image, it is preferable to perform the frame interpolationprocessing before the overdrive processing is performed. Note that oneexample of this embodiment is not limited to this.

In a similar manner, by performing overdrive processing after edgeenhancement processing is performed, response speed can be made high,the amount of overdrive can be controlled adequately, and display withfewer afterimages can be performed. Further, since the edge enhancementprocessing is processing for changing part of an image, an image whichis changed is generated by the processing. Thus, the gray level of eachpixel is changed. Therefore, by performing the overdrive processingafter the edge enhancement processing is performed, the overdriveprocessing can be changed in accordance with the amount of changegenerated by the edge enhancement processing. Accordingly, by performingthe overdrive processing after the edge enhancement processing isperformed, the amount of overdrive can be controlled adequately, so thatthe gray level of each pixel can be optimized. Thus, the response speedcan be made high and the overdrive can be accurately performed. Further,by the edge enhancement processing, clear display can be performed.Accordingly, in order to obtain a high-quality image, it is preferableto perform the edge enhancement processing before the overdriveprocessing is performed. Note that one example of this embodiment is notlimited to this.

Note that a variety of processings are further performed after theoverdrive processing is performed. After that, an image can bedisplayed.

Note that on a moving region of a screen, overdrive processing isperformed in many cases. In addition, on a static region of the screen,overdrive processing is hardly performed because afterimages are notgenerated. That is, in the screen, there are a region where overdriveprocessing is performed and a region where overdrive processing, is notperformed. In addition, such regions change over time. In the case ofperforming overdrive processing only on parts of regions in a screen inthis manner, there is an advantage such as improvement in processingspeed, reduction in power consumption, or improvement in processingaccuracy.

Further, super-resolution processing can be performed not on all regionsin a screen but on parts of the regions in the screen. In the case ofperforming super-resolution processing only on parts of regions in ascreen in this manner, there is an advantage such as improvement inprocessing speed, reduction in power consumption, improvement inprocessing accuracy, or reduction in image defects.

In the case where processing is performed on parts of regions in ascreen, in the screen, there are a first region where overdriveprocessing is performed and a second region where super-resolutionprocessing is performed. Further, a third region where neither of theprocessings is performed can be provided. Furthermore, a region wherethe first region and the second region do not overlap with each othercan be provided in the screen. Alternatively, a region where the firstregion and the second region overlap with each other can be provided inthe screen.

Thus, the region is considered in which the first region where theoverdrive processing is performed does not overlap with the secondregion where the super-resolution processing is performed. In this case,since the first region where the overdrive processing is performed is amoving region, the overdrive processing is performed in order to makeafterimages invisible. However, in such a moving region, even ifresolution is made high by super-resolution processing, it may bedifficult for eyes to recognize the resolution. Therefore, in such amoving region, super-resolution processing is not performed in somecases. Accordingly, in that case, it can be said that the region inwhich the first region where the overdrive processing is performed doesnot overlap with the second region where the super-resolution processingis performed is provided in some cases. Further in that case, the secondregion where the super-resolution processing is performed is a regionwhose detailed parts are preferably seen clearly. In the case where astatic image such as a still image is displayed, detailed parts can beseen clearly. Accordingly, it can be said that the region in which thefirst region where the overdrive processing is performed does notoverlap with the second region where the super-resolution processing isperformed is provided in some cases.

In the region in which the first region where the overdrive processingis performed overlaps with the second region where the super-resolutionprocessing is performed, response speed is high, an image with fewerafterimages is displayed, and detailed parts can be seen clearly. Thus,a realistic image can be displayed.

Thus far, the case has been described in which overdrive processing isperformed after super-resolution processing; however, processingperformed after the super-resolution processing is not limited to this.In a manner similar to the case of performing overdrive processing,local dimming processing of a backlight can be performed aftersuper-resolution processing. FIGS. 9C and 9D illustrate processing flowsof such a case. The processing flow in FIG. 9C corresponds to aprocessing flow where local dimming processing is added to theprocessing flow in FIG. 5A and a processing flow where frameinterpolation processing and local dimming processing are added to theprocessing flow in FIG. 1A. In a similar manner, the processing flow inFIG. 9D corresponds to a processing flow where local dimming processingis added to the processing flow in FIG. 5B and a processing flow whereframe interpolation processing and local dimming processing are added tothe processing flow in FIG. 1A. Therefore, the content or the drawingdescribed in the edge enhancement processing or the overdrive processingcan be applied to the case where local dimming processing of a backlightis performed in a similar manner. In a similar manner, the content orthe drawing described in the local dimming processing of a backlight canbe applied to the case where different processing is performed.

Here, the local dimming of a backlight is a technique by which displayis performed with the luminance of a backlight changed in each region ina screen. Therefore, depending on an image, the luminance of thebacklight is varied in each region in one screen. For example, in thecase where there is a region for displaying a low gray level in ascreen, the luminance of a backlight in the region is made low. Further,in the case where there is a region for displaying a high gray level inthe screen, the luminance of the backlight in the region is made high.Then, the transmittance of each pixel is determined in accordance withthe luminance of the backlight so that an accurate image can bedisplayed. Thus, in the region for displaying a low gray level in thescreen, the luminance of the backlight itself is low, so that adverseeffects of light leakage can be reduced. Therefore, in the case ofdisplaying a black image in such a region, the image can be displayed asa completely black image. In addition, in the region for displaying ahigh gray level in the screen, the luminance of the backlight itself ishigh, so that sufficiently bright display can be performed. Therefore,in the case of displaying a white image in such a region, luminance ismade higher than that in the case of displaying a normal white image,and the image can be displayed with higher peak luminance. Accordingly,contrast can be improved and a clear image can be displayed. Further,since the luminance of the backlight itself can be made low by localdimming, power consumption can be reduced. Thus, in order to performlocal dimming, there are processing for determining the luminance of abacklight in each region depending on an image to be displayed andprocessing for determining the transmittance of each pixel in accordancewith the luminance of the backlight so that the image to be displayedcan be accurately displayed. These processings or one of theseprocessings is referred to as local dimming processing. Therefore, inthe local dimming processing, after processing for determining theluminance of a backlight in each region is performed, processing fordetermining a video signal supplied to each pixel can be performed. Notethat one example of this embodiment is not limited to this. Thus, forexample, a processing flow in the case where the processing fordetermining the luminance of a backlight in each region and theprocessing for determining a video signal supplied to each pixel areseparately described can be illustrated as in each of FIGS. 10A to 10C.A processing flow in FIG. 10B corresponds to a processing flow wherelocal dimming processing as in FIG. 10A is added to the processing flowin FIG. 5A. A processing flow in FIG. 10C corresponds to a processingflow where local dimming processing as in FIG. 10A is added to theprocessing flow in FIG. 5B.

It is preferable that local dimming processing be performed aftersuper-resolution processing is performed in this manner. When thesuper-resolution processing is performed, due to restoration of data,new data is added. Thus, the gray level of each pixel is differentbefore and after the super-resolution processing in some cases.Alternatively, before and after the super-resolution processing, thereis a region where the gray level of a pixel is changed in a screen.Thus, by performing the local dimming after image data is restored bythe super-resolution processing, the local dimming processing can beaccurately performed. Therefore, contrast can be improved and anaccurate image can be displayed. Accordingly, in order to obtain ahigh-quality image, it is preferable to perform the super-resolutionprocessing before the local dimming processing is performed.Alternatively, in the local dimming processing, it is preferable toperform the super-resolution processing before the processing fordetermining the luminance of a backlight is performed. Alternatively, inthe local dimming processing, it is preferable to perform thesuper-resolution processing before the processing for determining avideo signal supplied to a pixel is performed. Note that one example ofthis embodiment is not limited to this.

Further, in the case of performing the local dimming processing, theluminance of the backlight is low. Thus, even when the transmittance ofthe pixel is slightly changed, the gray level of actual display is notchanged so much. On the other hand, in a state where the luminance ofthe backlight is low, a more detailed gradation can be expressed by thechange in the transmittance of the pixel. That is, the number of graylevels to be displayed can be increased. Therefore, by performing boththe local dimming processing and the super-resolution processing, ahigh-resolution image can be displayed with high power of expression, bywhich detailed parts can be perceived. In particular, gradation can beexpressed adequately in a region of a low gray level in the screen, anddisplay where gradation is crushed can be prevented.

Note that in a region where a gray level is low in a screen, localdimming processing is performed in many cases. In addition, in a regionwhere a gray level is high in the screen, i.e., a region where luminanceis high and bright display is performed, local dimming processing israrely performed because the luminance of a backlight is not easilylowered. That is, in the screen, there are a region where local dimmingprocessing is performed and a region where local dimming processing isnot performed. In addition, such regions change over time. In the caseof performing local dimming processing only on parts of regions in ascreen in this manner, there is an advantage such as improvement inprocessing speed, reduction in power consumption, or improvement inprocessing accuracy.

Further, super-resolution processing can be performed not on all regionsin a screen but on parts of the regions in the screen. In the case ofperforming super-resolution processing only on parts of regions in ascreen in this manner, there is an advantage such as improvement inprocessing speed, reduction in power consumption, improvement inprocessing accuracy, or reduction in image defects.

In the case where processing is performed on parts of regions in ascreen, in the screen, there are a first region where local dimmingprocessing is performed and the luminance of a backlight is lowered anda second region where super-resolution processing is performed. Further,a third region where neither the local dimming processing nor the superresolution processing is performed can be provided. Furthermore, aregion in which the first region where the local dimming processing isperformed and the luminance of the backlight is lowered does not overlapwith the second region where the super-resolution processing isperformed can be provided in the screen. Alternatively, a region wherethe first region and the second region overlap with each other can beprovided in the screen.

In the region in which the first region where the local dimmingprocessing is performed and the luminance of the backlight is loweredoverlaps with the second region where the super-resolution processing isperformed, contrast is high, an image can be displayed with smoothgradation expression, and detailed parts of the image can be clearlyseen. Thus, a realistic image can be displayed.

Note that in the case of performing local dimming processing, a screenis divided into a plurality of regions, and a backlight is provided ineach region. When the length (or the width) of the region or the pitchof the region is compared to the length (or the width) or the pitch of apixel included in a display device in which super-resolution processingis performed on parts of the regions of the screen and which displays aregion of a higher-resolution image, the length (or the width) of theregion of the backlight or the pitch of the region is preferably longerthan the length (or the width) or the pitch of the pixel included in thedisplay device in which the super-resolution processing is performed onparts of the regions of the screen and which displays the region of ahigher-resolution image. This is because in the case of performing thelocal dimming processing, an image is displayed by controlling not onlythe luminance of the backlight provided in each region but also thetransmittance of the pixel. Therefore, even in the case of displaying animage on which super-resolution processing is performed, ahigh-resolution image can be clearly displayed sufficiently when thepitch of each pixel is short, though the length (or the width) or thepitch of the region of the backlight is long.

Note that it is preferable that the screen be divided into a pluralityof regions where the luminance of the backlight is controlled; however,one example of this embodiment is not limited to this. The luminance ofthe entire screen can be controlled without division of the screen intoa plurality of regions.

In a similar manner, it is preferable that local dimming processing beperformed after frame interpolation processing is performed. Since theframe interpolation processing is processing for generating new framedata, an image which is changed is generated by the processing. Thus,the gray level of each pixel is changed. Alternatively, before and afterthe frame interpolation processing, there is a region where the graylevel of a pixel is changed in a screen. Therefore, by performing localdimming processing after new frame data is generated by frameinterpolation processing, the local dimming processing can be accuratelyperformed. Thus, contrast can be improved and an accurate image can bedisplayed. Accordingly, in order to obtain a high-quality image, it ispreferable to perform the frame interpolation processing before thelocal dimming processing is performed. Alternatively, in the localdimming processing, it is preferable to perform the frame interpolationprocessing before processing for determining the luminance of abacklight is performed. Alternatively, in the local dimming processing,it is preferable to perform the frame interpolation processing beforeprocessing for determining a video signal supplied to a pixel isperformed. Note that one example of this embodiment is not limited tothis.

In a similar manner, it is preferable that local dimming processing beperformed after edge enhancement processing is performed. Since the edgeenhancement processing is processing for changing part of an image, animage which is changed is generated by the processing. Thus, the graylevel of each pixel is changed. Therefore, by performing local dimmingprocessing after edge enhancement processing is performed, the localdimming processing can be accurately performed. Thus, contrast can beimproved and an accurate image can be displayed. Accordingly, in orderto obtain a high-quality image, it is preferable to perform the edgeenhancement processing before the local dimming processing is performed.Alternatively, in the local dimming processing, it is preferable toperform the edge enhancement processing before processing fordetermining the luminance of a backlight is performed. Alternatively, inthe local dimming processing, it is preferable to perform the edgeenhancement processing before processing for determining a video signalsupplied to a pixel is performed. Note that one example of thisembodiment is not limited to this.

FIGS. 9A to 9D each illustrate an example of the case where edgeenhancement processing, super-resolution processing, frame interpolationprocessing, and different processing (e.g., overdrive processing orlocal dimming processing of a backlight) are performed. Note that oneexample of this embodiment is not limited to this. In addition to theabove processings, processing such as overdrive processing or localdimming processing of a backlight can be performed. Therefore, in asimilar manner, any of the contents or the drawings described thus farcan be applied to the case where different processing is furtherperformed.

Note that a variety of processings are further performed after the localdimming processing is performed. After that, an image can be displayed.

Note that in the case where both local dimming processing and overdriveprocessing are performed, it is preferable that the overdrive processingbe performed after the local dimming processing is performed. Note thatone example of this embodiment is not limited to this. Note that beforeand after each stage in the processing flow, a variety of differentprocessings can be performed. As examples of a variety of differentprocessings, there are super-resolution processing, edge enhancementprocessing, frame interpolation processing, overdrive processing, localdimming processing, IP conversion processing, enlargement processing,and the like. Further, different processing is possible.

Therefore, in the case where overdrive processing is performed in FIG.9C, FIG. 9D, FIG. 10B, or FIG. 10C or in the case where local dimmingprocessing is performed in FIG. 9A or FIG. 9B, a processing flow as inFIG. 11A, FIG. 11B, FIG. 12A, or FIG. 12B is preferably used. Note thatone example of this embodiment is not limited to this.

By performing overdrive processing after frame interpolation processing,super-resolution processing, edge enhancement processing, and localdimming processing are performed in this manner, response speed can bemade high, the amount of overdrive can be controlled adequately, anddisplay with fewer afterimages can be performed. Alternatively, the graylevel of each pixel is changed in accordance with a change in luminanceof an image or a backlight by frame interpolation processing,super-resolution processing, edge enhancement processing, and localdimming processing; thus, overdrive processing can be changed inaccordance with the amount of a change in luminance. Therefore, byperforming the overdrive processing after the frame interpolationprocessing, the super-resolution processing, the edge enhancementprocessing, and the local dimming processing are performed, the amountof overdrive can be controlled adequately, so that the gray level ofeach pixel can be optimized. Thus, the response speed can be made highand the overdrive can be accurately performed. Further, by thesuper-resolution processing, a high-resolution image can be displayedwithout generation of afterimages. Furthermore, by the local dimmingprocessing, a high-contrast image can be displayed. Alternatively, bythe frame interpolation processing, afterimages can be reduced andmoving images can be accurately displayed. Alternatively, by the edgeenhancement processing, a clear image can be displayed. Accordingly, inorder to obtain a high-quality image, it is preferable to perform theframe interpolation processing, the super-resolution processing, theedge enhancement processing, and the local dimming processing before theoverdrive processing is performed. Note that one example of thisembodiment is not limited to this.

(Embodiment 5)

Next, the case where part of a processing flow is deformed is described.Therefore, the content described in any of the other embodiments can beapplied to, combined with, or replaced with this embodiment.

FIGS. 13A and 13B each illustrate an example of the case where part ofFIG. 10B, FIG. 10C, FIG. 12A, FIG. 12B, or the like is deformed.

First, super-resolution processing is performed in FIG. 13A.Concurrently, processing for controlling the luminance of a backlight inlocal dimming processing is performed using image data on whichsuper-resolution processing is not performed. Then, by using data whoseresolution is made high by super-resolution processing and data relatedto the determined luminance of each region of the backlight, which haslow resolution, processing for determining a video signal to be suppliedto each pixel in the local dimming processing is performed.

In the case of performing the super-resolution processing, an image isnot significantly changed before and after the processing in some cases.In addition, the pitch of the backlight is much larger than the pixelpitch. Therefore, even when processing for determining the luminance ofa backlight in each region in the local dimming processing is performedby using data before subjected to the super-resolution processing, thereis almost no practical problem.

By performing such processing, the super-resolution processing and theprocessing for controlling the luminance of a backlight in local dimmingprocessing can be concurrently performed. Thus, the total processingtime can be shortened. Accordingly, even in the case where real-timedisplay is needed, for example, in the case of displaying a game,display can be performed without delay.

For example, by using a multi-core CPU including a plurality of CPUcores and distributing processings across the CPU cores,super-resolution processing and local dimming processing can beperformed concurrently. With the use of a multi-core CPU in this manner,high-speed operation is possible with fewer components, Note that such amulti-core CPU can include a semiconductor device (or a transistor)formed using an SOI. With the use of an SOI, operation can be performedwith low power consumption and heat generation during the operation canbe suppressed.

Note that in FIG. 13A, edge enhancement processing, overdriveprocessing, frame interpolation processing, or the like can be added.For example, a flow chart in the case where edge enhancement processingis added is illustrated in FIG. 13B. Super-resolution processing isperformed after edge enhancement processing is performed. Note that oneexample of this embodiment is not limited to this.

FIGS. 14A and 14B each illustrate another example of the case where partof FIG. 10B, FIG. 10C, FIG. 12A, FIG. 12B, or the like is deformed.First, frame interpolation processing is performed in FIG. 14A.Concurrently, processing for controlling the luminance of a backlight inlocal dimming processing is performed using image data whose framefrequency has not been made high. Next, super-resolution processing isperformed using image data whose frame frequency has been made high bythe frame interpolation processing. Then, by using data whose resolutionis made high and data related to the determined luminance of each regionof the backlight, which has low resolution, processing for determining avideo signal supplied to each pixel in the local dimming processing isperformed.

Note that the super-resolution processing and the processing forcontrolling the luminance of a backlight in the local dimming processingcan be performed concurrently.

For example, by using a multi-core CPU including a plurality of CPUcores and distributing processings across the CPU cores, frameinterpolation processing, super-resolution processing, and local dimmingprocessing can be performed concurrently. With the use of a multi-coreCPU in this manner, high-speed operation is possible with fewercomponents. Note that such a multi-core CPU can include a semiconductordevice (or a transistor) formed using an SOI. With the use of an SOI,operation can be performed with low power consumption and heatgeneration during the operation can be suppressed.

In the case of performing the frame interpolation processing, an imageis not significantly changed before and after the processing in somecases. In addition, the pitch of the backlight is much larger than thepixel pitch. Therefore, even when processing for determining theluminance of a backlight in each region in the local dimming processingis performed by using data before subjected to the frame interpolationprocessing, there is almost no practical problem.

By performing such processing, the frame interpolation processing andthe processing for controlling the luminance of a backlight in localdimming processing can be concurrently performed. Thus, the totalprocessing time can be shortened. Accordingly, even in the case wherereal-time display is needed, for example, in the case of displaying agame, display can be performed without delay.

Note that in FIG. 14.A, edge enhancement processing, overdriveprocessing, or the like can be added. For example, FIG. 14B illustratesan example of the case where edge enhancement processing is alsoperformed. In FIG. 14B, edge enhancement processing is performed afterframe interpolation processing. Note that one example of this embodimentis not limited to this. The edge enhancement processing can be performedbefore the frame interpolation processing.

Note that for example, in FIG. 14A, the super-resolution processing canbe performed using a plurality of processing systems. FIGS. 15A and 15Billustrate examples of such a case. FIG. 15A corresponds to a processingflow to which the processing flow in FIG. 6A or FIG. 6B is applied. FIG.15B corresponds to a processing flow to which the processing flow inFIG. 7B is applied. FIGS. 16A and 16B illustrate examples of the casewhere the super-resolution processing is performed using a plurality ofprocessing systems also in FIG. 14B. FIG. 16A illustrates the case wheresuper-resolution processing is performed using a plurality of processingsystems after edge enhancement processing. FIG. 16B illustrates the casewhere edge enhancement processing is performed using data subjected toframe interpolation processing and data before, subjected to frameinterpolation processing. Therefore, in FIG. 16B, the edge enhancementprocessing can be performed using a plurality of processing systems.Note that one example of this embodiment is not limited to this.

The content described in any of the other embodiments can be applied tothis embodiment as described above. The other contents can be applied ina similar manner.

(Embodiment 6)

In this embodiment, examples of lighting devices are described. Thelighting device can be used as a backlight of a liquid crystal displaydevice, an interior lamp, or the like. Note that one example of thisembodiment is not limited to this.

FIGS. 17A and 17B illustrate a backlight or a lighting device in thecase where a point light source is used. As illustrated in FIG. 17A, adevice 1001 includes a plurality of point light sources 1002. Byarranging the point light sources 1002 in array, a uniform planar lightsource can be formed. The device 1001 can be used as a backlight of aliquid crystal display device or part of the backlight of the liquidcrystal display device.

In addition, partitions 1003 are arranged in a lateral direction.Further, partitions 1004 are arranged in a longitudinal direction. Byarranging the plurality of partitions 1003 and the plurality ofpartitions 1004, the planar light source can be divided into a pluralityof regions. In FIG. 17A, the planar light source is divided into threeregions in the longitudinal direction and is divided into nine regionsin the lateral direction. Therefore, light can be prevented from leakinginto a different region by the partitions. Further, by controlling theluminance of the point light source 1002 in each region, local dimming(local dimming of a backlight) can be realized. In particular, byarranging the partitions, light can be prevented from leaking into adifferent region, so that the luminance of each region can be accuratelycontrolled. Therefore, the transmittance of a liquid crystal element ineach region can be easily derived. Alternatively, contrast can beimproved because of little light leakage. Note that one example of thisembodiment is not limited to this.

Alternatively, some of the light sources can be set to be in anon-lighting state and the non-lighting state can be moved line by lineor block by block in a screen. That is, the point light sources in thescreen can be party turned off and the off-state regions can be scanned.For example, the point light sources can be scanned from the top to thebottom. By performing such backlight scanning, afterimages can bereduced and moving-image characteristics can be improved.

Note that as the partitions, only partitions which are arranged in alateral direction like the partitions 1003 can be arranged.Alternatively, as the partitions, only partitions which are arranged ina longitudinal direction like the partitions 1004 can be arranged.Alternatively, it is possible not to provide a partition itself.

Note that it is preferable that a surface of the partition 1003 or thepartition 1004 be a mirror surface or a white surface. Note that oneexample of this embodiment is not limited to this. In the case of themirror surface, light can be reflected, so that light can be efficientlyutilized. Therefore, power consumption can be reduced. In the case ofthe white surface, light can be diffused. Therefore, boundaries betweenregions are not easily seen, so that visibility can be improved.

Note that the transmittance of the partition 1003 or the partition 1004is preferably less than or equal to 50%, more preferably less than orequal to 30%. Alternatively, the transmittance of the partition 1003 orthe partition 1004 is preferably greater than or equal to 1%, morepreferably greater than or equal to 5%. Note that one example of thisembodiment is not limited to this. Because of low transmittance, lightleakage can be reduced and the luminance of each region can beaccurately controlled. However, in the case where light does not passcompletely, the boundaries between the regions are seen, so thatvisibility is decreased in some cases. Therefore, when a slight amountof light passes, the boundaries between the regions are not easily seen,so that visibility can be improved.

Note that the partition 1003 or the partition 1004 can be formed usingan organic matter such as acrylic, plastics, polycarbonate, or PET. Notethat one example of this embodiment is not limited to this.

Note that a spacer 1005 can be provided. Note that one example of thisembodiment is not limited to this. It is possible not to provide thespacer 1005. The spacer 1005 has a function of preventing a sheetprovided over the point light sources 1002, the partitions 1003, thepartitions 1004, and the like from bending.

Note that in the case of providing the spacer 1005, the number of thespacers 1005 is not so large but can be small. Therefore, in FIG. 17A,the planar light source is divided into three regions in thelongitudinal direction and is divided into nine regions in the lateraldirection, so that twenty seven regions are provided in total. It ispossible to provide regions where the spacers 1005 are provided andregions where the spacers 1005 are not provided. Alternatively, thenumber of the spacers 1005 can be smaller than the number of theregions. In the case where the spacers 1005 are not provided in all theregions in this manner, manufacture can be facilitated and/or cost canbe reduced.

Note that it is preferable that the spacer 1005 be a transparent spacer,a black spacer, or a white spacer. With the transparent spacer, theblack spacer, or the white spacer, generation of unevenness in luminanceor deviation of color depending on existence and nonexistence of thespacer 1005 can be suppressed. Note that one example of this embodimentis not limited to this.

Note that the spacer 1005 can be formed using an organic matter such asacrylic, plastics, polycarbonate, or PET. Note that one example of thisembodiment is not limited to this.

Note that for example, the point light source 1002 is formed usinglight-emitting diodes of three colors or lasers of three colors. Inaddition, the light-emitting diodes or the lasers have colors of red,blue, and green. Further, for example, by using the lasers of threecolors, a white color can be expressed. Therefore, colors are notlimited to red, blue, and green as long as a white color can beexpressed. For example, cyan, magenta, yellow, and the like (CMYK) canbe used for the point light source.

In the case where luminance can be controlled in each color in thismanner, local dimming can be performed more precisely. Thus, powerconsumption can be reduced or contrast can be improved, for example.

Note that the number of light-emitting diodes of each color ispreferably the same. Note that one example of this embodiment is notlimited to this. Only the number of light-emitting diodes of a certaincolor can be increased. For example, the number of green light-emittingdiodes can be twice the number of red or blue light-emitting diodes. Bychanging the number of light-emitting diodes in each color in thismanner, chromaticity can be easily adjusted. Further, a difference inthe life of light-emitting diodes between the respective colors can besuppressed.

Note that colors of the light-emitting diodes are not limited to threecolors. For example, by using a light-emitting diode having a colorwhich is similar to a certain color, chromaticity can be increased. Forexample, four colors can be used by addition of a color which is similarto green to red, blue, and green.

Note that a white light-emitting diode can be used in addition to a redlight-emitting diode, a blue light-emitting diode, and a greenlight-emitting diode. By using the white light-emitting diode, the livesof the light-emitting diodes can be prolonged. Alternatively, by usingthe white light-emitting diode, the change in color due to temperaturecan be suppressed.

Note that it is possible to use only a white light-emitting diode andnot to use a light-emitting diode other than the white light-emittingdiode, such as a red light-emitting diode, a blue light-emitting diode,or a green light-emitting diode. By using only the white light-emittingdiode, colors can be prevented from not being mixed with each other.Alternatively, by using only the white light-emitting diode, deviationof color due to deterioration can be suppressed.

Note that a pitch 1007 of the point light source 1002 in the lateraldirection is preferably shorter than a pitch 1006 of the point lightsource 1002 in the longitudinal direction. Note that one example of thisembodiment is not limited to this.

Note that as for the number of regions, the number of regions in thelateral direction is preferably larger than the number of regions in thelongitudinal direction. For example, the number of regions in thelongitudinal direction is three and the number of regions in the lateraldirection is nine in FIG. 17A.

Note that the number of regions in one screen is preferably smaller thanthe number of light-emitting diodes of a certain color. That is, as fora certain color in one region, a plurality of point light sources arepreferably provided. As for the point light sources provided in oneregion, the luminance of the plurality of point light sources of acertain color is preferably controlled so as to be the same luminance atthe same time. That is, luminance is preferably controlled in each colorin one region. For example, in the case where three red light-emittingdiodes are provided in one region, it is preferable that the luminanceof the three light-emitting diodes be raised when the luminance israised and the luminance of the three light-emitting diodes be loweredwhen the luminance is lowered. However, since characteristics oflight-emitting diodes or the like vary, it is difficult to make thelight-emitting diode have the same luminance. Therefore, it ispreferable that the light-emitting diodes emit light at the sameluminance in consideration of variations in characteristics. Forexample, it is preferable that the light-emitting diodes emit light atthe same luminance in consideration of a variation of approximately 30%.By providing a plurality of point light sources in one region in thismanner, unevenness in luminance can be suppressed. Alternatively,deterioration of the point light sources can be suppressed. Note thatone example of this embodiment is not limited to this.

FIG. 17B illustrates an example of part of a cross section in FIG. 17A.A diffusing plate 1011 is provided over the device 1001. Unevenness inluminance is suppressed by the diffusing plate 1011. The diffusing plate1011 is supported by the spacers 1005 so as not to bend even in thecenter of the screen.

A display panel 1012 is provided over the diffusing plate 1011. Thedisplay panel includes, for example, a pixel, a driver circuit, a liquidcrystal element, a glass substrate, a thin film transistor, apolarization plate, a retardation plate, a color filter, and/or a prismsheet. By operating the display panel 1012 in cooperation with thebacklight, appropriate display can be performed.

Note that the diffusing plate 1011 has a function of diffusing lightwhile transmitting light. Thus, it is preferable that the diffusingplate 1011 have a function of diffusing light and have hightransmittance. Therefore, the transmittance of the diffusing plate 1011is preferably higher than the transmittance of the partition 1003. Whenthe transmittance of the diffusing plate 1011 is high, light reflectedon the partition 1003 can be transmitted through the diffusing plate1011. Thus, light can be prevented from leaking into a different regionand can be easily emitted to the screen. Therefore, luminance in eachregion can be precisely controlled and local dimming can be accuratelyperformed. Note that one example of this embodiment is not limited tothis.

Note that height 1014 of the partition 1003 is preferably higher thanheight 1013 of the point light source 1002. In order to prevent lightemitted from the point light source 1002 from leaking into a differentregion, the height 1014 of the partition 1003 is preferably higher thanthe height 1013 of the point light source 1002. Note that one example ofthis embodiment is not limited to this.

Note that a distance 1015 between the partition 1003 and the diffusingplate 1011 is preferably shorter than the height 1014 of the partition1003. In the case where the distance 1015 is long, a large amount oflight leaks. Therefore, the distance 1015 is preferably shorter than theheight 1014 of the partition 1003. Note that one example of thisembodiment is not limited to this.

Note that the distance 1015 between the partition 1003 and the diffusingplate 1011 is preferably longer than the height 1013 of the point lightsource 1002. In the case where the distance 1015 is too short,boundaries between regions may be seen on the screen because theboundaries are sharp. Therefore, in order that the boundaries betweenthe regions are not seen on the screen, length for leakage of some lightis needed. Thus, by making the height 1014 of the partition 1003 higherthan the height 1013 of the point light source 1002, an appropriateamount of light can leak. Note that one example of this embodiment isnot limited to this.

Note that it is preferable that the height 1014 of the partition 1003 besubstantially the same as the height of the point light source 1002.Description “substantially the same” refers to the case where twoobjects have the same values in consideration of an error inmanufacturing, variation, or a slight difference. For example, avariation of approximately 10% can be included. By making the height ofthe partition be substantially the same as the height of the point lightsource 1002, the amount of light leakage can be uniform, so thatunevenness in luminance can be suppressed. Note that one example of thisembodiment is not limited to this.

Note that although the point light source is provided in each region inFIGS. 17A and 17B, one example of this embodiment is not limited tothis. A small planar light source can be provided in each region. FIGS.18A to 18D illustrate an example of the case where a planar light sourceis provided in each region. The planar light source can be formed in amanner similar to that in the case of point light source. Therefore, thecontent (may be part of the content) or the diagram (may be part of thediagram) described in FIGS. 17A and 17B can be applied to FIGS. 18A to18D.

In FIG. 18A, a planar light source 1102 is provided in each region. Theplanar light source 1102 can be realized with a variety of structures.

Note that although FIG. 18A illustrates the case where the partition1003 and the partition 1004 are not provided, one example of thisembodiment is not limited to this. Only partitions which are arranged ina lateral direction like the partitions 1003 can be arranged.Alternatively, only partitions which are arranged in a longitudinaldirection like the partitions 1004 can be arranged. Alternatively, it ispossible to provide both of the partitions.

Note that the spacer 1005 can be provided. Note that one example of thisembodiment is not limited to this. It is possible not to provide thespacer 1005. The spacer 1005 has a function of preventing a sheetprovided over the planar light sources 1102 and the like from bending.Note that in the case of the planar light source, the area of a void ina region is small, so that it is possible not to provide the spacer1005.

Note that the pitch of the planar light source 1102 in the lateraldirection is preferably shorter than the pitch of the planar lightsource 1102 in the longitudinal direction. Note that one example of thisembodiment is not limited to this.

Note that in the case where the partition is provided, the height of thepartition is preferably higher than the height of the planar lightsource 1102. In order to prevent light emitted from the planar lightsource 1102 from leaking into a different region, the height of thepartition is preferably higher than the height of the planar lightsource 1102. Note that one example of this embodiment is not limited tothis.

Further, in the case where a diffusing plate is provided over the planarlight source 1102, a distance between the partition and the diffusingplate is preferably longer than the height of the planar light source1102. In the case where the distance is too short, boundaries betweenregions may be seen on a screen because the boundaries are sharp.Therefore, in order that the boundaries between the regions are not seenon the screen, length for leakage of some light is needed. Thus, bymaking the height of the partition higher than the height of the planarlight source 1102, an appropriate amount of light can leak. Note thatone example of this embodiment is not limited to this.

Next, as an example of the planar light source 1102. FIG. 18Billustrates a cross section in the case where a light guide plate and aline light source (or a group of point light sources) are provided and asmall planar light source is formed. FIG. 18B illustrates a crosssection of three planar light sources. Light enters a light guide plate1104 from a line light source 1103. Light is fully reflected in thelight guide plate 1104 repeatedly and is transmitted. In addition, abottom surface 1105 of the light guide plate 1104 is processed.Therefore, light is emitted from a surface of the light guide plate1104, so that a planar light source is realized.

For example, the bottom surface 1105 is processed as follows: unevennessis formed like a prism, or ink is printed. By controlling density,shape, or the like thereof, a uniform planar light source can berealized.

Note that in the case where a planar light source as in FIG. 18A isused, the diffusing plate 1011 can be provided over the planar lightsource. Thus, unevenness in luminance can be suppressed. Note thatunlike the case of using a point light source, in the case of using theplanar light source 1102, luminance has already been uniformed to someextent. Thus, it is possible not to provide the diffusing plate 1011.

As another example of the planar light source 1102, a plane fluorescenttube (plane cathode tube) can be used.

Alternatively, as illustrated in FIG. 18C, a fluorescent tube (cathodetube) 1106 is bent and provided in a region so as to be used like aplane fluorescent tube (plane cathode tube). Thus, a planar light sourcecan be realized. In that case, as illustrated in a cross-sectional viewin FIG. 18D, by providing a diffusing plate 1107 around the fluorescenttube (cathode tube) 1106, in particular, above the fluorescent tube(cathode tube) 1106, it is possible to make the planar light sourcecloser to a uniform planar light source. Note that one example of thisembodiment is not limited to this.

(Embodiment 7)

Next, another structure example and a driving method of a display deviceare described. In this embodiment, the case of using a display deviceincluding a display element whose luminance response with respect tosignal writing is slow (response time is long) is described. In thisembodiment, a liquid crystal element is described as an example of thedisplay element with long response time. In this embodiment, a liquidcrystal element is illustrated as an example of the display element withlong response time. However, a display element in this embodiment is notlimited to this, and a variety of display elements whose luminanceresponse with respect to signal writing is slow can be used.

In a general liquid crystal display device, luminance response withrespect to signal writing is slow, and it sometimes takes more than oneframe period to complete the response even when signal voltage iscontinuously applied to a liquid crystal element. Moving images cannotbe displayed precisely by such a display element. Further, in the caseof active matrix driving, time for signal writing to one liquid crystalelement is only a period (one scan line selection period) obtained bydividing a signal writing cycle (one frame period or one subframeperiod) by the number of scan lines, and the liquid crystal elementcannot respond in such a short time in many cases. Therefore, most ofthe response of the liquid crystal element is performed in a periodduring which signal writing is not performed. Here, the dielectricconstant of the liquid crystal element is changed in accordance with thetransmittance of the liquid crystal element, and the response of theliquid crystal element in a period during which signal writing is notperformed means that the dielectric constant of the liquid crystalelement is changed in a state where electric charge is not exchangedwith the outside of the liquid crystal element (in a constant chargestate). In other words, in a formula wherecharge=(capacitance)·(voltage), the capacitance is changed in a statewhere the charge is constant. Accordingly, voltage applied to the liquidcrystal element is changed from voltage in signal writing, in accordancewith the response of the liquid crystal element. Therefore, in the casewhere the liquid crystal element whose luminance response with respectto signal writing is slow is driven by active matrix driving, voltageapplied to the liquid crystal element cannot theoretically reach thevoltage in signal writing.

In the display device in this embodiment, a signal level in signalwriting is corrected in advance (a correction signal is used) so that adisplay element can reach desired luminance within a signal writingcycle. Thus, the above problem can be solved. Further, since theresponse time of the liquid crystal element becomes shorter as thesignal level becomes higher, the response time of the liquid crystalelement can also be shorter by writing a correction signal. A drivingmethod by which such a correction signal is added is referred to asoverdrive. By overdrive in this embodiment, even when a signal writingcycle is shorter than a cycle for an image signal input to the displaydevice (an input image signal cycle T_(in)), the signal level iscorrected in accordance with the signal writing cycle, so that thedisplay element can reach desired luminance within the signal writingcycle. The case where the signal writing cycle is shorter than the inputimage signal cycle T_(in) is, for example, the case where one originalimage is divided into a plurality of subimages and the plurality ofsubimages are sequentially displayed in one frame period.

Next, an example of correcting a signal level in signal writing in adisplay device driven by active matrix driving is described withreference to FIGS. 19A and 19B. FIG. 19A is a graph schematicallyillustrating a time change in signal level in signal writing in onedisplay element, with the time as the horizontal axis and the signallevel in signal writing as the vertical axis. FIG. 19B is a graphschematically illustrating a time change in display level, with the timeas the horizontal axis and the display level as the vertical axis. Notethat when the display element is a liquid crystal element, the signallevel in signal writing can be voltage, and the display level can be thetransmittance of the liquid crystal element. In the followingdescription, the vertical axis in FIG. 19A is regarded as the voltage,and the vertical axis in FIG. 19B is regarded as the transmittance. Notethat in the overdrive in this embodiment, the signal level may be otherthan the voltage (may be a duty ratio or current, for example). Notethat in the overdrive in this embodiment, the display level may be otherthan the transmittance (may be luminance or current, for example).Liquid crystal elements are classified into two modes: a normally blackmode in which black is displayed when voltage is 0 (e.g., a VA mode andan IPS mode), and a normally white mode in which white is displayed whenvoltage is 0 (e.g., a TN mode and an OCB mode). The graph illustrated inFIG. 19B corresponds to both of the modes. The transmittance increasesas the value of the vertical axis becomes larger in the normally blackmode, and the transmittance increases as the value of the vertical axisbecomes smaller in the normally white mode. That is, a liquid crystalmode in this embodiment may be either a normally black mode or anormally white mode. Note that timing of signal writing is representedon the time axis by dotted lines, and a period after signal writing isperformed until the next signal writing is performed is referred to as aretention period F_(i). In this embodiment, i is an integer and an indexfor representing each retention period. In FIGS. 19A and 19B, i is 0 to2; however, i can be an integer other than 0 to 2 (only the case where iis 0 to 2 is illustrated). Note that in the retention period F_(i),transmittance for realizing luminance corresponding to an image signalis denoted by T_(i), and voltage for providing the transmittance T_(i)in a constant state is denoted by V_(i). In FIG. 19A, a dashed line 5101represents a time change in voltage applied to the liquid crystalelement in the case where overdrive is not performed, and a solid line5102 represents a time change in voltage applied to the liquid crystalelement in the case where the overdrive in this embodiment is performed.In a similar manner, in FIG. 19B, a dashed line 5103 represents a timechange in transmittance of the liquid crystal element in the case whereoverdrive is not performed, and a solid line 5104 represents a timechange in transmittance of the liquid crystal element in the case wherethe overdrive in this embodiment is performed. Note that a differencebetween the desired transmittance T_(i) and the actual transmittance atthe end of the retention period F_(i) is referred to as an error α_(i).

It is assumed that, in the graph illustrated in FIG. 19A, both thedashed line 5101 and the solid line 5102 represent the case wheredesired voltage V₀ is applied in a retention period F₀; and in the graphillustrated in FIG. 19B, both the dashed line 5103 and the solid line5104 represent the case where desired transmittance T₀ is obtained. Inthe case where overdriving is not performed, desired voltage V₁ isapplied at the beginning of a retention period F₁ as shown by the dashedline 5101. As has been described above, a period for signal writing ismuch shorter than a retention period, and the liquid crystal element isin a constant charge state in most of the retention period. Accordingly,voltage applied to the liquid crystal element in the retention period F₁is changed along with a change in transmittance and is greatly differentfrom the desired voltage V₁ at the end of the retention period F₁. Inthis case, the dashed line 5103 in the graph of FIG. 19B is greatlydifferent from desired transmittance T₁. Accordingly, accurate displayof an image signal cannot be performed, so that image quality isdecreased. On the other hand, in the case where the overdrive in thisembodiment is performed, voltage V₁′ which is higher than the desiredvoltage V₁ is applied to the liquid crystal element at the beginning ofthe retention period F₁ as shown by the solid line 5102. That is, thevoltage V₁′ which is corrected from the desired voltage V₁ is applied tothe liquid crystal element at the beginning of the retention period F₁so that the voltage applied to the liquid crystal element at the end ofthe retention period F₁ is close to the desired voltage V₁ inanticipation of a gradual change in voltage applied to the liquidcrystal element in the retention period F₁. Thus, the desired voltage V₁can be accurately applied to the liquid crystal element. In this case,as shown by the solid line 5104 in the graph of FIG. 19B, the desiredtransmittance T₁ can be obtained at the end of the retention period F₁.In other words, the response of the liquid crystal element within thesignal writing cycle can be realized, despite the fact that the liquidcrystal element is in a constant charge state in most of the retentionperiod. Then, in a retention period F₂, the case where desired voltageV₂ is lower than V₁ is described. Also in that case, as in the retentionperiod F₁, voltage V₂′ which is corrected from the desired voltage V₂may be applied to the liquid crystal element at the beginning of theretention period F₂ so that the voltage applied to the liquid crystalelement at the end of the retention period F₂ is close to the desiredvoltage V₂ in anticipation of a gradual change in voltage applied to theliquid crystal element in the retention period F₂. Thus, as shown by thesolid line 5104 in the graph of FIG. 19B, desired transmittance T₂ canbe obtained at the end of the retention period F₂. Note that in the casewhere V_(i) is higher than V_(i−1) as in the retention period F₁, thecorrected voltage V_(i)′ is preferably corrected so as to be higher thandesired voltage V_(i). Further, when V_(i) is lower than as in theretention period F₂, the corrected voltage V_(i)′ is preferablycorrected so as to be lower than the desired voltage V_(i). Note that aspecific correction value can be derived by measuring responsecharacteristics of the liquid crystal element in advance. As a method ofrealizing overdrive in a device, a method by which a correction formulais formulated and included in a logic circuit, a method by which acorrection value is stored in a memory as a look-up table and is read asnecessary, or the like can be used.

Note that there are several limitations on realization of the overdrivein this embodiment in a device. For example, voltage correction has tobe performed in the range of the rated voltage of a source driver. Thatis, in the case where desired voltage is originally high and idealcorrection voltage exceeds the rated voltage of the source driver, notall the correction can be performed. Problems in such a case aredescribed with reference to FIGS. 19C and 19D. As in FIG. 19A, FIG. 19Cis a graph in which a time change in voltage in one liquid crystalelement is schematically illustrated as a solid line 5105 with the timeas the horizontal axis and the voltage as the vertical axis. As in FIG.19B, FIG. 19D is a graph in which a time change in transmittance of oneliquid crystal element is schematically illustrated as a solid line 5106with the time as the horizontal axis and the transmittance as thevertical axis. Note that since other references are similar to those inFIGS. 19A and 19B, description thereof is omitted. FIGS. 19C and 19Dillustrate a state where sufficient correction cannot be performedbecause the correction voltage V₁′ for realizing the desiredtransmittance T₁ in the retention period F₁ exceeds the rated voltage ofthe source driver; thus V₁′=V₁ has to be given. In this case, thetransmittance at the end of the retention period F₁ is deviated from thedesired transmittance T₁ by the error α₁. Note that the error α₁ isincreased only when the desired voltage is originally high; therefore, adecrease in image quality due to occurrence of the error α₁ is in theallowable range in many cases. However, as the error α₁ is increased, anerror in algorithm for voltage correction is also increased. In otherwords, in the algorithm for voltage correction, when it is assumed thatthe desired transmittance is obtained at the end of the retentionperiod, even though the error α₁ is increased, voltage correction isperformed on the basis that the error α₁ is small. Accordingly, theerror is included in correction in the following retention period F₂;thus, an error α₂ is also increased. Further, in the case where theerror α₂ is increased, the following error α₃ is further increased, forexample, and the error is increased in a chain reaction manner, whichresults in a significant decrease in image quality. In the overdrive inthis embodiment, in order to prevent increase of errors in such a chainreaction manner, when the correction voltage V_(i)′ exceeds the ratedvoltage of the source driver in the retention period F_(i), an errorα_(i) at the end of the retention period F_(i) is estimated, and thecorrection voltage in a retention period F_(i+1) can be adjusted inconsideration of the amount of the error α_(i). Thus, even when theerror α_(i) is increased, the effect of the error α_(i) on the errorα_(i+1) can be minimized, so that increase of errors in a chain reactionmanner can be prevented. An example where the error α₂ is minimized inthe overdrive in this embodiment is described with reference to FIGS.19E and 19F. In a graph of FIG. 19E, a solid line 5107 represents a timechange in voltage in the case where the correction voltage V₂′ in thegraph of FIG. 19C is further adjusted to be correction voltage V₂″. Agraph of FIG. 19F illustrates a time change in transmittance in the casewhere voltage is corrected in accordance with the graph of FIG. 19E. Thesolid line 5106 in the graph of FIG. 19D indicates that excessivecorrection is caused by the correction voltage V₂′. On the other hand,the solid line 5108 in the graph of FIG. 19F indicates that excessivecorrection is suppressed by the correction voltage V₂″ which is adjustedin consideration of the error α₁ and the error α₂ is minimized. Notethat a specific correction value can be derived from measuring responsecharacteristics of the liquid crystal element in advance. As a method ofrealizing overdrive in a device, a method by which a correction formulais formulated and included in a logic circuit, a method by which acorrection value is stored in a memory as a look-up table and read asnecessary, or the like can be used. Further, such a method can be addedseparately from a portion for calculating correction voltage V_(i)′ orcan be included in the portion for calculating correction voltageV_(i)′. Note that the amount of correction of correction voltage V_(i)″which is adjusted in consideration of an error α_(i−1) difference withthe desired voltage V_(i)) is preferably smaller than that of V_(i)′.That is, |V_(i)′″−V_(i)|<|V_(i)′−V_(i)| is preferable.

Note that the error α_(i) which is caused because ideal correctionvoltage exceeds the rated voltage of the source driver is increased as asignal writing cycle becomes shorter. This is because the response timeof the liquid crystal element needs to be shorter as the signal writingcycle becomes shorter, so that higher correction voltage is necessary.Further, as a result of an increase in correction voltage needed, thecorrection voltage exceeds the rated voltage of the source driver morefrequently, so that the large error α_(i) occurs more frequently.Therefore, it can be said that the overdrive in this embodiment becomesmore effective as the signal writing cycle becomes shorter.Specifically, the overdrive in this embodiment is significantlyeffective in the case of performing the following driving methods: adriving method by which one original image is divided into a pluralityof subimages and the plurality of subimages are sequentially displayedin one frame period, a driving method by which motion of an image isdetected from a plurality of images and an intermediate image of theplurality of images is generated and inserted between the plurality ofimages (so-called motion compensation frame rate doubling), and adriving method in which such driving methods are combined, for example.

Note that the rated voltage of the source driver has the lower limit inaddition to the upper limit described above. An example of the lowerlimit is the case where voltage which is lower than the voltage 0 cannotbe applied. In this case, since ideal correction voltage cannot beapplied as in the case of the upper limit described above, the errorα_(i) is increased. However, also in that case, the error α_(i) at theend of the retention period F_(i) is estimated, and the correctionvoltage in the retention period F_(i+1) can be adjusted in considerationof the amount of the error α_(i) in a manner similar to the abovemethod. Note that in the case where voltage which is lower than thevoltage 0 (negative voltage) can be applied as the rated voltage of thesource driver, the negative voltage may be applied to the liquid crystalelement as correction voltage. Thus, the voltage applied to the liquidcrystal element at the end of retention period F_(i) can be adjusted soas to be close to the desired voltage V_(i) in anticipation of a changein potential due to a constant charge state.

Note that in order to suppress deterioration of the liquid crystalelement, so-called inversion driving by which the polarity of voltageapplied to the liquid crystal element is periodically inverted can beperformed in combination with the overdrive. That is, the overdrive inthis embodiment includes the case where the overdrive is performed atthe same time as the inversion driving. For example, in the case wherethe length of the signal writing cycle is half of that of the inputimage signal cycle T_(in), when the length of a cycle for invertingpolarity is the same or substantially the same as that of the inputimage signal cycle T_(in), two sets of writing of a positive signal andtwo sets of writing of a negative signal are alternately performed. Thelength of the cycle for inverting polarity is made larger than that ofthe signal writing cycle in this manner, so that the frequency of chargeand discharge of a pixel can be reduced. Thus, power consumption can bereduced. Note that when the cycle for inverting polarity is made toolong, a defect in which luminance difference due to the difference ofpolarity is recognized as a flicker occurs in some cases; therefore, itis preferable that the length of the cycle for inverting polarity besubstantially the same as or smaller than that of the input image signalcycle T_(in).

(Embodiment 8)

Next, another structure example and a driving method of a display deviceare described. In this embodiment, a method is described by which animage for interpolating motion of an image input from the outside of adisplay device (an input image) is generated inside the display devicein response to a plurality of input images and the generated image (thegeneration image) and the input image are sequentially displayed. Notethat when an image for interpolating motion of an input image is ageneration image, motion of moving images can be made smooth, and adecrease in quality of moving images because of afterimages or the likedue to hold driving can be suppressed. Here, moving image interpolationis described below. Ideally, display of moving images is realized bycontrolling the luminance of each pixel in real time; however,individual control of pixels in real time has problems such as theenormous number of control circuits, space for wirings, and the enormousamount of input image data. Thus, it is difficult to realize theindividual control of pixels. Therefore, for display of moving images bya display device, a plurality of still images are sequentially displayedin a certain cycle so that display appears to be moving images. Thecycle (in this embodiment, referred to as an input image signal cycleand denoted by T_(in)) is standardized, and for example, 1/60 second inNTSC and 1/50 second in PAL. Such a cycle does not cause a problem ofmoving image display in a CRT, which is an impulsive display device.However, in a hold-type display device, when moving images conforming tothese standards are displayed without change, a defect in which displayis blurred because of afterimages or the like due to hold driving (holdblur) occurs. Since hold blur is recognized by discrepancy betweenunconscious motion interpolation due to human eyes tracking andhold-type display, the hold blur can be reduced by making the inputimage signal cycle shorter than that in conventional standards (bymaking the control closer to individual control of pixels in real time).However, it is difficult to reduce the length of the input image signalcycle because the standard needs to be changed and the amount of data isincreased. However, an image for interpolating motion of an input imageis generated inside the display device in response to a standardizedinput image signal, and display is performed while the generation imageinterpolates the input image, so that hold blur can be reduced without achange in the standard or an increase in the amount of data. Operationsuch that an image signal is generated inside the display device inresponse to an input image signal to interpolate motion of the inputimage is referred to as moving image interpolation.

By a method for interpolating moving images in this embodiment, motionblur can be reduced. The method for interpolating moving images in thisembodiment can include an image generation method and an image displaymethod. Further, by using a different image generation method and/or adifferent image display method for motion with a specific pattern,motion blur can be effectively reduced. FIGS. 20A and 20B are schematicdiagrams each illustrating an example of a method for interpolatingmoving images in this embodiment. FIGS. 20A and 20B each illustratetiming of treating each image by using the position of the horizontaldirection, with the time as the horizontal axis. A portion representedas “input” indicates timing at which an input image signal is input.Here, images 5121 and 5122 are focused as two images that are temporallyadjacent. An input image is input at an interval of the cycle T_(in).Note that the length of one cycle T_(in) is referred to as one frame orone frame period in some cases. A portion represented as “generation”indicates timing at which a new image is generated from an input imagesignal. Here, an image 5123 which is a generation image generated inresponse to the images 5121 and 5122 is focused. A portion representedas “display” indicates timing at which an image is displayed in thedisplay device. Note that images other than the focused images are onlyrepresented by dashed lines, and by treating such images in a mannersimilar to that of the focused images, the example of the method forinterpolating moving images in this embodiment can be realized.

In the example of the method for interpolating moving images in thisembodiment, as illustrated in FIG. 20A, a generation image which isgenerated in response to two input images that are temporally adjacentis displayed in a period after one image is displayed until the otherimage is displayed, so that moving image interpolation can be performed.In this case, a display cycle of a display image is preferably half ofan input cycle of the input image. Note that the display cycle is notlimited to this and can be a variety of display cycles. For example, inthe case where the length of the display cycle is shorter than half ofthat of the input cycle, moving images can be displayed more smoothly.Alternatively, in the case where the length of the display cycle islonger than half of that of the input cycle, power consumption can bereduced. Note that here, an image is generated in response to two inputimages which are temporally adjacent; however, the number of inputimages serving as a basis is not limited to two and can be othernumbers. For example, when an image is generated in response to three(may be more than three) input images which are temporally adjacent, ageneration image with higher accuracy can be obtained as compared to thecase where an image is generated in response to two input images. Notethat the display timing of the image 5121 is the same as the inputtiming of the image 5122, that is, the display timing is one frame laterthan the input timing. However, display timing in the method forinterpolating moving images in this embodiment is not limited to thisand can be a variety of display timings. For example, the display timingcan be delayed with respect to the input timing by more than one frame.Thus, the display timing of the image 5123 which is the generation imagecan be delayed, which allows enough time to generate the image 5123 andleads to reduction in power consumption and manufacturing cost. Notethat when the display timing is delayed with respect to the input timingfor a long time, a period for holding an input image becomes longer, andthe memory capacity which is necessary for holding the input image isincreased. Therefore, the display timing is preferably delayed withrespect to the input timing by approximately one to two frames.

Here, an example of a specific generation method of the image 5123 whichis generated in response to the images 5121 and 5122 is described. If isnecessary to detect motion of an input image in order to interpolatemoving images. In this embodiment, a method called a block matchingmethod can be used in order to detect motion of an input image. Notethat this embodiment is not limited to this, and a variety of methods(e.g., a method for obtaining a difference of image data or a method ofusing Fourier transformation) can be used. In the block matching method,first, image data for one input image (here, image data of the image5121) is stored in a data storage means (e.g., a memory circuit such asa semiconductor memory or a RAM). Then, an image in the next frame(here, the image 5122) is divided into a plurality of regions. Note thatthe divided regions can have the same rectangular shapes as illustratedin FIG. 20A; however, the divided regions are not limited to them andcan have a variety of shapes (e.g., the shape or size varies dependingon images). After that, in each divided region, data is compared to theimage data in the previous frame (here, the image data of the image5121), which is stored in the data storage means, so that a region wherethe image data is similar to each other is searched. The example of FIG.20A illustrates that the image 5121 is searched for a region where datais similar to that of a region 5124 in the image 5122, and a region 5126is found. Note that a search range is preferably limited when the image5121 is searched. In the example of FIG. 20A, a region 5125 which isapproximately four times larger than the region 5124 is set as thesearch range. By making the search range larger than this, detectionaccuracy can be increased even in a moving image with high-speed motion.Note that search in an excessively wide range needs an enormous amountof time, which makes it difficult to realize detection of motion. Thus,the region 5125 has preferably approximately two to six times largerthan the area of the region 5124. After that, a difference of theposition between the searched region 5126 and the region 5124 in theimage 5122 is obtained as a motion vector 5127. The motion vector 5127represents motion of image data in the region 5124 in one frame period.Then, in order to generate an image illustrating the intermediate stateof motion, an image generation vector 5128 obtained by changing the sizeof the motion vector without a change in the direction thereof isgenerated, and image data included in the region 5126 of the image 5121is moved in accordance with the image generation vector 5128, so thatimage data in a region 5129 of the image 5123 is generated. Byperforming a series of processings on the entire region of the image5122, the image 5123 is generated. Then, by sequentially displaying theimage 5121, the image 5123, and the image 5122, moving images can beinterpolated. Note that the position of an object 5130 in the image isdifferent (i.e., the object is moved) between the images 5121 and 5122.In the generated image 5123, the object is located at the midpointbetween the images 5121 and 5122. By displaying such images, motion ofmoving images can be made smooth, and blur of moving images due toafterimages or the like can be reduced.

Note that the size of the image generation vector 5128 can be determinedin accordance with the display timing of the image 5123. In the exampleof FIG. 20A, since the display timing of the image 5123 is the midpoint(½) between the display timings of the images 5121 and 5122, the size ofthe image generation vector 5128 is half of that of the motion vector5127. Alternatively, for example, when the display timing is ⅓ betweenthe display timings of the images 5121 and 5122, the size of the imagegeneration vector 5128 can be ⅓, and when the display timing is ⅔between the display timings of the images 5121 and 5122, the size can be⅔.

Note that in the case where a new image is generated by moving aplurality of regions having different motion vectors in this manner, aportion where one region has already been moved to a region that is adestination for another region or a portion to which any region is notmoved is generated in some cases (i.e., overlap or blank occurs in somecases). For such portions, data can be compensated. As a method forcompensating an overlap portion, a method by which overlap data isaveraged; a method by which data is arranged in order of priorityaccording to the direction of motion vectors or the like, andhigh-priority data is used as data in a generation image; or a method bywhich one of color and brightness is arranged in order of priority andthe other thereof is averaged can be used, for example. As a method forcompensating a blank portion, a method by which image data of theportion of the image 5121 or the image 5122 is used as data in ageneration image without modification, a method by which image data ofthe portion of the image 5121 or the image 5122 is averaged, or the likecan be used. Then, the generated image 5123 is displayed in accordancewith the size of the image generation vector 5128, so that motion ofmoving images can be made smooth, and the decrease in quality of movingimages because of afterimages or the like due to hold driving can besuppressed.

In another example of the method for interpolating moving images in thisembodiment, as illustrated in FIG. 20B, when a generation image which isgenerated in response to two input images which are temporally adjacentis displayed in a period after one image is displayed until the otherimage is displayed, each display image is divided into a plurality ofsubimages to be displayed. Thus, moving images can be interpolated. Thiscase can have advantages of displaying a dark image at regular intervals(advantages when a display method is made close to impulsive display) inaddition to advantages of a shorter image display cycle. That is, blurof moving images due to afterimages or the like can be further reducedas compared to the case where the length of the image display cycle isjust made to half of that of the image input cycle. In the example ofFIG. 20B, “input” and “generation” can be similar to the processings inthe example of FIG. 20A; therefore, description thereof is omitted. For“display” in the example of FIG. 20B, one input image and/or onegeneration image can be divided into a plurality of subimages to bedisplayed. Specifically, as illustrated in FIG. 20B, the image 5121 isdivided into subimages 5121 a and 5121 b and the subimages 5121 a and5121 b are sequentially displayed so as to make human eyes perceive thatthe image 5121 is displayed; the image 5123 is divided into subimages5123 a and 5123 b and the subimages 5123 a and 5123 b are sequentiallydisplayed so as to make human eyes perceive that the image 5123 isdisplayed; and the image 5122 is divided into subimages 5122 a and 5122b and the subimages 5122 a and 5122 b are sequentially displayed so asto make human eyes perceive that the image 5122 is displayed. That is,the display method can be made close to impulsive display while theimage perceived by human eyes is similar to that in the example of FIG.20A, so that blur of moving images due to afterimages or the like can befurther reduced. Note that the number of division of subimages is two inFIG. 20B; however, the number of division of subimages is not limited tothis and can be other numbers. Note that subimages are displayed atregular intervals (½) in FIG. 20B; however, timing of displayingsubimages is not limited to this and can be a variety of timings. Forexample, when timing of displaying dark subimages 5121 b, 5122 b, and5123 b is made earlier (specifically, timing at ¼ to ½), the displaymethod can be made much closer to impulsive display, so that blur ofmoving images due to afterimages or the like can be further reduced.Alternatively, when the timing of displaying dark subimages is delayed(specifically, timing at ½ to ¾), the length of a period for displayinga bright image can be increased, so that display efficiency can beincreased and power consumption can be reduced.

Another example of the method for interpolating moving images in thisembodiment is an example in which the shape of an object which is movedin an image is detected and different processings are performeddepending on the shape of the moving object. FIG. 20C illustratesdisplay timing as in the example of FIG. 20B and the case where movingcharacters (also referred to as scrolling texts, subtitles, captions, orthe like) are displayed. Note that since terms “input” and “generation”may be similar to those in FIG. 20B, they are not illustrated in FIG.20C. The amount of blur of moving images by hold driving variesdepending on properties of a moving object in some cases. In particular,blur is recognized remarkably when characters are moved in many cases.This is because eyes track moving characters to read the characters, sothat hold blur easily occur. Further, since characters have clearoutlines in many cases, blur due to hold blur is further emphasized insome cases. That is, determining whether an object which is moved in animage is a character and performing special processing when the objectis the character are effective in reducing hold blur. Specifically, whenedge detection, pattern detection, and/or the like are/is performed onan object which is moved in an image and the object is determined to bea character, motion compensation is performed even on subimagesgenerated by division of one image so that an intermediate state ofmotion is displayed. Thus, motion can be made smooth. In the case wherethe object is determined not to be a character, when subimages aregenerated by division of one image as illustrated in FIG. 20B, thesubimages can be displayed without a change in the position of themoving object. The example of FIG. 20C illustrates the case where aregion 5131 determined to be characters is moved upward, and theposition of the region 5131 is different between the subimages 5121 aand 5121 b. In a similar manner, the position of the region 5131 isdifferent between the subimages 5123 a and 5123 b, and between thesubimages 5122 a and 5122 b. Thus, motion of characters for which holdblur is particularly easily recognized can be made smoother than that bynormal motion compensation frame rate doubling, so that blur of movingimages due to afterimages or the like can be further reduced.

(Embodiment 9)

In this embodiment, structures and operation of a pixel which can beused in a liquid crystal display device are described. Note that as theoperation mode of a liquid crystal element in this embodiment, a TN(twisted nematic) mode, an IPS (in-plane-switching) mode, an FFS (fringefield switching) mode, an MVA (multi-domain vertical alignment) mode, aPVA (patterned vertical alignment) mode, an ASM (axially symmetricaligned macrocell) mode, an OCB (optically compensated birefringence)mode, an FLC (ferroelectric liquid crystal) mode, an AFLC(anti-ferroelectric liquid crystal) mode, or the like can be used.

FIG. 21A illustrates an example of a pixel structure which can be usedin the liquid crystal display device. A pixel 5080 includes a transistor5081, a liquid crystal element 5082, and a capacitor 5083. A gate of thetransistor 5081 is electrically connected to a wiring 5085. A firstterminal of the transistor 5081 is electrically connected to a wiring5084. A second terminal of the transistor 5081 is electrically connectedto a first terminal of the liquid crystal element 5082. A secondterminal of the liquid crystal element 5082 is electrically connected toa wiring 5087. A first terminal of the capacitor 5083 is electricallyconnected to the first terminal of the liquid crystal element 5082. Asecond terminal of the capacitor 5083 is electrically connected to awiring 5086. Note that a first terminal of a transistor is one of asource and a drain, and a second terminal of the transistor is the otherof the source and the drain. That is, when the first terminal of thetransistor is the source, the second terminal of the transistor is thedrain. In a similar manner, when the first terminal of the transistor isthe drain, the second terminal of the transistor is the source.

The wiring 5084 can serve as a signal line. The signal line is a wiringfor transmitting signal voltage, which is input from the outside of thepixel, to the pixel 5080. The wiring 5085 can serve as a scan line. Thescan line is a wiring for controlling on/off of the transistor 5081. Thewiring 5086 can serve as a capacitor line. The capacitor line is awiring for applying predetermined voltage to the second terminal of thecapacitor 5083. The transistor 5081 can serve as a switch. The capacitor5083 can serve as a storage capacitor. The storage capacitor is acapacitor with which the signal voltage is continuously applied to theliquid crystal element 5082 even when the switch is off. The wiring 5087can serve as a counter electrode. The counter electrode is a wiring forapplying predetermined voltage to the second terminal of the liquidcrystal element 5082. Note that the function of each wiring is notlimited to this, and each wiring can have a variety of functions. Forexample, by changing voltage applied to the capacitor line, voltageapplied to the liquid crystal element can be adjusted. Note that it isacceptable as long as the transistor 5081 serves as a switch, and thetransistor 5081 may be either a p-channel transistor or an n-channeltransistor.

FIG. 21B illustrates an example of a pixel structure which can be usedin the liquid crystal display device. The example of the pixel structureillustrated in FIG. 21B is the same as that in FIG. 21A except that thewiring 5087 is eliminated and the second terminal of the liquid crystalelement 5082 and the second terminal of the capacitor 5083 areelectrically connected to each other. The example of the pixel structureillustrated in FIG. 21B can be particularly used in the case of using ahorizontal electric field mode (including an IPS mode and an FFS mode)liquid crystal element. This is because in the horizontal electric fieldmode liquid crystal element, the second terminal of the liquid crystalelement 5082 and the second terminal of the capacitor 5083 can be formedover the same substrate, so that it is easy to electrically connect thesecond terminal of the liquid crystal element 5082 and the secondterminal of the capacitor 5083 to each other. With the pixel structureas illustrated in FIG. 21B, the wiring 5087 can be eliminated, so that amanufacturing process can be simplified and manufacturing cost can bereduced.

A plurality of pixel structures illustrated in FIG. 21A or FIG. 21B canbe arranged in matrix. Thus, a display portion of a liquid crystaldisplay device is formed, and a variety of images can be displayed, FIG.21C illustrates a circuit structure in the case where a plurality ofpixel structures illustrated in FIG. 21A are arranged in matrix. FIG.21C is a circuit diagram illustrating four pixels among a plurality ofpixels included in the display portion. A pixel arranged in an i-thcolumn and a j-th row (each of i and j is a natural number) isrepresented as a pixel 5080_i, j, and a wiring 5084_i, a wiring 5085_j,and a wiring 5086_j are electrically connected to the pixel 5080_i, j.In a similar manner, a wiring 5084_i+1, the wiring 5085_j, and thewiring 5086_j are electrically connected to a pixel 5080_i+1, j. In asimilar manner, the wiring 5084_j, a wiring 5085_j+1, and a wiring5086_j+1 are electrically connected to a pixel 5080_i, j+1. In a similarmanner, the wiring 5084_i+1, the wiring 5085_j+1, and the wiring5086_j+1 are electrically connected to a pixel 5080_i+1, j+1. Note thateach wiring can be used in common with a plurality of pixels in the samerow or the same column. In the pixel structure illustrated in FIG. 21C,the wiring 5087 is a counter electrode, which is used by all the pixelsin common; therefore, the wiring 5087 is not indicated by the naturalnumber i or j. Note that since the pixel structure in FIG. 21B can alsobe used, the wiring 5087 is not required even in a structure where thewiring 5087 is provided and can be eliminated when another wiring servesas the wiring 5087, for example.

The pixel structure in FIG. 21C can be driven by a variety of methods.In particular, when the pixels are driven by a method called AC drive,deterioration (burn-in) of the liquid crystal element can be suppressed.FIG. 21D is a timing chart of voltage applied to each wiring in thepixel structure in FIG. 21C in the case where dot inversion driving,which is a kind of AC drive, is performed. By the dot inversion driving,flickers seen when the AC drive is performed can be suppressed.

In the pixel structure in FIG. 21C, a switch in a pixel electricallyconnected to the wiring 5085_j is selected (in an on state) in a j-thgate selection period in one frame period and is not selected (in an offstate) in the other periods. Then, a (j+1)th gate selection period isprovided after the j-th gate selection period. By performing sequentialscanning in this manner, all the pixels are sequentially selected in oneframe period. In the timing chart of FIG. 21D, the switch in the pixelis selected when the level of voltage is high (high level), and theswitch is not selected when the level of the voltage is low (low level).Note that this is the case where the transistor in each pixel is ann-channel transistor. In the case of using a p-channel transistor, arelationship between voltage and a selection state is opposite to thatin the case of using an n-channel transistor.

In the timing chart illustrated in FIG. 21D, in the j-th gate selectionperiod in a k-th frame (k is a natural number), positive signal voltageis applied to the wiring 5084_i used as a signal line, and negativesignal voltage is applied to the wiring 5084_i+1. Then, in the (j+l)thgate selection period in the k-th frame, negative signal voltage isapplied to the wiring 5084_i, and positive signal voltage is applied tothe wiring 5084_i+1. After that, signals whose polarities are invertedevery gate selection period are alternately supplied to the signal line.Accordingly, in the k-th frame, the positive signal voltage is appliedto the pixels 5080_i, j and 5080_i+1, j+1, and the negative signalvoltage is applied to the pixels 5080_i+1, j and 5080_i, j+1. Then, in a(k+1)th frame, signal voltage whose polarity is opposite to that of thesignal voltage written in the k-th frame is written to each pixel.Accordingly, in the (k+1)th frame, the positive signal voltage isapplied to the pixels 5080_i+1, j and 5080_i, j+1, and the negativesignal voltage is applied to the pixels 5080_i, j and 5080_i+1, j+1. Inthis manner, the dot inversion driving is a driving method by whichsignal voltage whose polarity is different between adjacent pixels isapplied in the same frame and the polarity of the voltage signal for thepixel is inverted every one frame. By the dot inversion driving,flickers seen when the entire or part of an image to be displayed isuniform can be suppressed while deterioration of the liquid crystalelement is suppressed. Note that voltage applied to all the wirings 5086including the wirings 5086_j and 5086_j+1 can be fixed voltage. Notethat although only the polarity of the signal voltage for the wirings5084 is illustrated in the timing chart, the signal voltage can actuallyhave a variety of levels in the polarity illustrated. Note that here,the case where the polarity is inverted per dot (per pixel) isdescribed; however, this embodiment is not limited to this, and thepolarity can be inverted per a plurality of pixels. For example, thepolarity of signal voltage to be written is inverted per two gateselection periods, so that power consumed in writing signal voltage canbe reduced. Alternatively, the polarity can be inverted per column(source line inversion) or per row (gate line inversion).

Note that fixed voltage may be applied to the second terminal of thecapacitor 5083 in the pixel 5080 in one frame period. Here, since thelevel of voltage applied to the wiring 5085 used as a scan line is lowlevel in most of one frame period, which means that substantiallyconstant voltage is applied to the wiring 5085; therefore, the secondterminal of the capacitor 5083 in the pixel 5080 may be connected to thewiring 5085. FIG. 21E illustrates an example of a pixel structure whichcan be used in the liquid crystal display device. Compared to the pixelstructure in FIG. 21C, a feature of the pixel structure in FIG. 21E liesin that the wiring 5086 is eliminated and the second terminal of thecapacitor 5083 in the pixel 5080 and the wiring 5085 in the previous roware electrically connected to each other. Specifically, in the rangeillustrated in FIG. 21E, the second terminals of the capacitors 5083 inthe pixels 5080_i, j+1 and 5080_i+1, j+1 are electrically connected tothe wiring 5085_j. By electrically connecting the second terminal of thecapacitor 5083 in the pixel 5080 and the wiring 5085 in the previous rowto each other in this manner, the wiring 5086 can be eliminated, so thatthe aperture ratio of the pixel can be increased. Note that the secondterminal of the capacitor 5083 may be connected to the wiring 5085 inanother row instead of in the previous row. Note that the pixelstructure in FIG. 21E can be driven by a driving method which is similarto that in the pixel structure in FIG. 21C.

Note that voltage applied to the wiring 5084 used as a signal line canbe lowered by using the capacitor 5083 and the wiring electricallyconnected to the second terminal of the capacitor 5083. A pixelstructure and a driving method in this case are described with referenceto FIGS. 21F and 21G. Compared to the pixel structure in FIG. 21A, afeature of the pixel structure in FIG. 21F lies in that two wirings 5086are provided per pixel column, and in adjacent pixels, one wiring iselectrically connected to every other second terminal of the capacitors5083 and the other wiring is electrically connected to the remainingevery other second terminal of the capacitors 5083. Note that twowirings 5086 are referred to as a wiring 5086-1 and a wiring 5086-2.Specifically, in the range illustrated in FIG. 21F, the second terminalof the capacitor 5083 in the pixel 5080_1, j is electrically connectedto a wiring 5086-1_j; the second terminal of the capacitor 5083 in thepixel 5080_i+1, j is electrically connected to a wiring 5086-2_j; thesecond terminal of the capacitor 5083 in the pixel 5080_i, j+1 iselectrically connected to a wiring 5086-2_j+1; and the second terminalof the capacitor 5083 in the pixel 5080_i+1, j+1 is electricallyconnected to a wiring 5086-1_j+1.

For example, when positive signal voltage is written to the pixel5080_i, j in the k-th frame as illustrated in FIG. 21G, the wiring5086-1_j becomes a low level, and is changed to a high level after thej-th gate selection period. Then, the wiring 5086-1_j is kept at a highlevel in one frame period, and after negative signal voltage is writtenin the j-th gate selection period in the (k+1)th frame, the wiring5086-1_j is changed to a high level. In this manner, voltage of thewiring which is electrically connected to the second terminal of thecapacitor 5083 is changed in a positive direction after positive signalvoltage is written to the pixel, so that voltage applied to the liquidcrystal element can be changed in the positive direction by apredetermined level. That is, signal voltage written to the pixel can belowered by the predetermined level, so that power consumed in signalwriting can be reduced. Note that when negative signal voltage iswritten in the j-th gate selection period, voltage of the wiring whichis electrically connected to the second terminal of the capacitor 5083is changed in a negative direction after negative signal voltage iswritten to the pixel. Thus, voltage applied to the liquid crystalelement can be changed in the negative direction by a predeterminedlevel, and the signal voltage written to the pixel can be reduced as inthe ease of the positive polarity. In other words, as for the wiringwhich is electrically connected to the second terminal of the capacitor5083, different wirings are preferably used for a pixel to whichpositive signal voltage is applied and a pixel to which negative signalvoltage is applied in the same row of the same frame. FIG. 21Fillustrates an example in which the wiring 5086-1 is electricallyconnected to the pixel to which positive signal voltage is applied inthe k-th frame and the wiring 5086-2 is electrically connected to thepixel to which negative signal voltage is applied in the k-th frame.Note that this is just an example, and for example, in the case of usinga driving method by which pixels to which positive signal voltage iswritten and pixels to which negative signal voltage is written appearevery two pixels, it is preferable to perform electrical connectionswith the wirings 5086-1 and 5086-2 alternately every two pixels.Further, in the case where signal voltage of the same polarity iswritten to all the pixels in one row (gate line inversion), one wiring5086 may be provided per row. In other words, in the pixel structure inFIG. 21C, the driving method by which signal voltage written to a pixelis lowered as described with reference to FIGS. 21F and 21G can be used.

Next, a pixel structure and a driving method which are preferably usedparticularly in the case where the mode of a liquid crystal element is avertical alignment (VA) mode typified by an MVA mode and a PVA mode. TheVA mode has advantages such as no rubbing step in manufacture, littlelight leakage at the time of black display, and low driving voltage, buthas a problem in that image quality is decreased (the viewing angle isnarrower) when a screen is seen from an oblique angle. In order to widenthe viewing angle in the VA mode, a pixel structure where one pixelincludes a plurality of subpixels as illustrated in FIGS. 22A and 22B iseffective. Pixel structures illustrated in FIGS. 22A and 22B areexamples of the case where the pixel 5080 includes two subpixels (asubpixel 5080-1 and a subpixel 5080-2). Note that the number ofsubpixels in one pixel is not limited to two and can be other numbers.The viewing angle can be further widened as the number of subpixelsbecomes larger. A plurality of subpixels can have the same circuitstructure. Here, all the subpixels have the circuit structureillustrated in FIG. 21A. Note that the first subpixel 5080-1 includes atransistor 5081-1, a liquid crystal element 5082-1, and a capacitor5083-1. The connection relation of each element is the same as that inthe circuit structure in FIG. 21A. In a similar manner, the secondsubpixel 5080-2 includes a transistor 5081-2, a liquid crystal element5082-2, and a capacitor 5083-2. The connection relation of each elementis the same as that in the circuit structure in FIG. 21A.

The pixel structure in FIG. 22A includes, for two subpixels included inone pixel, two wirings 5085 (a wiring 5085-1 and a wiring 5085-2) usedas scan lines, one wiring 5084 used as a signal line, and one wiring5086 used as a capacitor line. When the signal line and the capacitorline are shared between two subpixels in this manner, the aperture ratiocan be improved. Further, since a signal line driver circuit can besimplified, manufacturing cost can be reduced. Furthermore, since thenumber of connections between a liquid crystal panel and a drivercircuit IC can be reduced, yield can be improved. The pixel structure inFIG. 22B includes, for two subpixels included in one pixel, one wiring5085 used as a scan line, two wirings 5084 (a wiring 5084-1 and a wiring5084-2) used as signal lines, and one wiring 5086 used as a capacitorline. When the scan line and the capacitor line are shared between twosubpixels in this manner, the aperture ratio can be improved. Further,since the total number of scan lines can be reduced, the length of eachgate line selection period can be sufficiently increased even in ahigh-definition liquid crystal panel, and appropriate signal voltage canbe written to each pixel.

FIGS. 22C and 22D illustrate an example in which the liquid crystalelement in the pixel structure in FIG. 22B is replaced with the shape ofa pixel electrode and the electrical connection of each element isschematically illustrated. In FIGS. 22C and 22D, an electrode 5088-1corresponds to a first pixel electrode, and an electrode 5088-2corresponds to a second pixel electrode. In FIG. 22C, the first pixelelectrode 5088-1 corresponds to a first terminal of the liquid crystalelement 5082-1 in FIG. 22B, and the second pixel electrode 5088-2corresponds to a first terminal of the liquid crystal element 5082-2 inFIG. 22B. That is, the first pixel electrode 5088-1 is electricallyconnected to one of a source and a drain of the transistor 5081-1, andthe second pixel electrode 5088-2 is electrically connected to one of asource and a drain of the transistor 5081-2. Meanwhile, in FIG. 22D, theconnection relation between the pixel electrode and the transistor isopposite to that in FIG. 22C. That is, the first pixel electrode 5088-1is electrically connected to one of the source and the drain of thetransistor 5081-2, and the second pixel electrode 5088-2 is electricallyconnected to one of the source and the drain of the transistor 5081-1.

By alternately arranging a plurality of pixel structures as illustratedin FIG. 22C and FIG. 22D in matrix, special advantageous effects can beobtained. FIGS. 22E and 22F illustrate examples of the pixel structureand a driving method thereof. In the pixel structure in FIG. 22E, aportion corresponding to the pixels 5080_i, j and 5080_i+1, j+1 has thestructure illustrated in FIG. 22C, and a portion corresponding to thepixels 5080_i+1, j and 5080_i, j+1 has the structure illustrated in FIG.22D. In this structure, by performing driving as the timing chartillustrated in FIG. 22F, in the j-th gate selection period in the k-thframe, positive signal voltage is written to the first pixel electrodein the pixel 5080_i, j and the second pixel electrode in the pixel5080_i+1, j, and negative signal voltage is written to the second pixelelectrode in the pixel 5080_i, j and the first pixel electrode in thepixel 5080_i+1, j. In the (j+1)th gate selection period in the k-thframe, positive signal voltage is written to the second pixel electrodein the pixel 5080_i, j+1 and the first pixel electrode in the pixel5080_i+1, j+1, and negative signal voltage is written to the first pixelelectrode in the pixel 5080_i, j+1 and the second pixel electrode in thepixel 5080_i+1, j+1. In the (k+1)th frame, the polarity of signalvoltage is inverted in each pixel. Thus, the polarity of voltage appliedto the signal line can be the same in one frame period while drivingcorresponding to dot inversion driving is realized in the pixelstructure including subpixels. Therefore, power consumed in writingsignal voltage to the pixels can be drastically reduced. Note thatvoltage applied to all the wirings 5086 including the wirings 5086_j and5086_j+1 can be fixed voltage.

Further, by a pixel structure and a driving method illustrated in FIGS.22G and 22H, the level of signal voltage written to a pixel can belowered. In the structure, capacitors lines which are electricallyconnected to a plurality of subpixels included in each pixel aredifferent between the subpixels. That is, by using the pixel structureand the driving method illustrated in FIGS. 22G and 22H, subpixels towhich voltages having the same polarities are written in the same frameshare a capacitor line in the same row, and subpixels to which voltageshaving different polarities are written in the same frame use differentcapacitor lines in the same row. Then, when writing in each row isterminated, voltage of the capacitor lines is changed to the positivedirection in the subpixels to which positive signal voltage is written,and changed to the negative direction in the subpixels to which negativesignal voltage is written. Thus, the level of the signal voltage writtento the pixel can be lowered. Specifically, two wirings 5086 (the wirings5086-1 and 5086-2) used as capacitor lines are provided in each row. Thefirst pixel electrode in the pixel 5080_i,j and the wiring 5086-1_j areelectrically connected to each other through the capacitor. The secondpixel electrode in the pixel 5080_i, j and the wiring 5086-2_j areelectrically connected to each other through the capacitor. The firstpixel electrode in the pixel 5080_i+1, j and the wiring 5086-2_j areelectrically connected to each other through the capacitor. The secondpixel electrode in the pixel 5080_i+1,j and the wiring 5086-1_j areelectrically connected to each other through the capacitor. The firstpixel electrode in the pixel 5080_i, j+1 and the wiring 5086-2_j+1 areelectrically connected to each other through the capacitor. The secondpixel electrode in the pixel 5080_i, j+1 and the wiring 5086-1_j+1 areelectrically connected to each other through the capacitor. The firstpixel electrode in the pixel 5080_i+1, j+1 and the wiring 5086-1_j+1 areelectrically connected to each other through the capacitor. The secondpixel electrode in the pixel 5080_i+1, j+1 and the wiring 5086-2_j+1 areelectrically connected to each other through the capacitor. Note thatthis is just an example, and for example, in the case of using a drivingmethod by which pixels to which positive signal voltage is written andpixels to which negative signal voltage is written appear every twopixels, it is preferable to perform electrical connections with thewirings 5086-1 and 5086-2 alternately every two pixels. Further, in thecase where signal voltage of the same polarity is written in all thepixels in one row (gate line inversion), one wiring 5086 may be providedper row. In other words, in the pixel structure in FIG. 22E, the drivingmethod by which signal voltage written to a pixel is lowered asdescribed with reference to FIGS. 22G and 22H can be used.

(Embodiment 10)

In this embodiment, examples of display devices are described.

First, an example of a system block of a liquid crystal display deviceis described with reference to FIG. 23A. The liquid crystal displaydevice includes a circuit 5361, a circuit 5362, a circuit 5363_1, acircuit 5363_2, a pixel portion 5364, a circuit 5365, and a lightingdevice 5366. A plurality of wirings 5371 which are extended from thecircuit 5362 and a plurality of wirings 5372 which are extended from thecircuit 5363_1 and the circuit 5363_2 are provided in the pixel portion5364. In addition, pixels 5367 which include display elements such asliquid crystal elements are provided in matrix in respective regionswhere the plurality of wirings 5371 and theplurality of wirings 5372intersect with each other.

The circuit 5361 has a function of outputting a signal, voltage,current, or the like to the circuit 5362, the circuit 5363_1, thecircuit 5363_2, and the circuit 5365 in response to a video signal 5360and can serve as a controller, a control circuit, a timing generator, apower supply circuit, a regulator, or the like. In this embodiment, forexample, the circuit 5361 supplies a signal line driver circuit startsignal (SSP), a signal line driver circuit clock signal (SCK), a signalline driver circuit inverted clock signal (SCKB), video signal data(DATA), or a latch signal (LAT) to the circuit 5362. Alternatively, forexample, the circuit 5361 supplies a scan line driver circuit startsignal (GSP), a scan line driver circuit clock signal (GCK), or a scanline driver circuit inverted clock signal (GCKB) to the circuit 5363_1and the circuit 5363_2. Alternatively, the circuit 5361 outputs abacklight control signal (BLC) to the circuit 5365. Note that thisembodiment is not limited to this. The circuit 5361 can supply a varietyof signals, voltages, currents, or the like to the circuit 5362, thecircuit 5363_1, the circuit 5363_2, and the circuit 5365.

Note that in the circuit 5361, super-resolution processing, edgeenhancement processing, frame interpolation processing, overdriveprocessing, local dimming processing. IP conversion processing, and/orenlargement processing can be performed, for example.

Note that in the circuit 5365, local dimming processing or the like canbe performed. Alternatively, in the circuit 5365, processing fordetermining the luminance of a backlight in each region in local dimmingprocessing can be performed.

Note that in the circuit 5361 or the circuit 5365, a variety ofprocessings can be performed. Therefore, the circuit 5361 or the circuit5365 can include more circuits. That is, the circuit 5361 or the circuit5365 can be formed using a plurality of circuits. In that case, theplurality of circuits included in the circuit 5361 or the circuit 5365can be formed over one IC chip. Note that one example of this embodimentis not limited to this. The plurality of circuits included in thecircuit 5361 or the circuit 5365 can be formed over a plurality ofdifferent IC chips. In that case, the circuit 5361 or the circuit 5365can be formed using a plurality of IC chips.

In that case, the circuit 5362 has a function of outputting videosignals to the plurality of wirings 5371 in response to a signalsupplied from the circuit 5361 (e.g., SSP, SCK, SCKB, DATA, or LAT) andcan serve as a signal line driver circuit. The circuit 5363_1 and thecircuit 5363_2 each have a function of outputting scan signals to theplurality of wirings 5372 in response to a signal supplied from thecircuit 5361 (e.g., GSP, GCK, or GCKB) and can serve as a scan linedriver circuit. The circuit 5365 has a function of controlling theluminance (or average luminance) of the lighting device 5366 bycontrolling the amount of electric power supplied to the lighting device5366, time to supply the electric power to the lighting device 5366, orthe like in response to the backlight control signal (BLC) and can serveas a power supply circuit.

Note that in the case where video signals are input to the plurality ofwirings 5371, the plurality of wirings 5371 can serve as signal lines,video signal lines, source lines, or the like. In the case where scansignals are input to the plurality of wirings 5372, the plurality ofwirings 5372 can serve as signal lines, scan lines, gate lines, or thelike. Note that one example of this embodiment is not limited to this.

Note that in the case where the same signal is input to the circuit5363_1 and the circuit 5363_2 from the circuit 5361, scan signals outputfrom the circuit 5363_1 to the plurality of wirings 5372 and scansignals output from the circuit 5363_2 to the plurality of wirings 5372have approximately the same timings in many cases. Therefore, loadcaused by driving of the circuit 5363_1 and the circuit 5363_2 can bereduced. Accordingly, the display device can be made large.Alternatively, the display device can have higher definition.Alternatively, since the channel width of transistors included in thecircuit 5363_1 and the circuit 5363_2 can be decreased, a display devicewith a narrower frame can be obtained. Note that this embodiment is notlimited to this. The circuit 5361 can supply different signals to thecircuit 5363_1 and the circuit 5363_2.

Note that one of the circuit 5363_1 and the circuit 5363_2 can beeliminated.

Note that a wiring such as a capacitor line, a power supply line, or ascan line can be additionally provided in the pixel portion 5364. Then,the circuit 5361 can output a signal, voltage, or the like to such awiring. Alternatively, a circuit which is similar to the circuit 5363_1or the circuit 5363_2 can be additionally provided. The additionallyprovided circuit can output a signal such as a scan signal to theadditionally provided wiring.

Note that the pixel 5367 can include a light-emitting element such as anEL element as a display element. In this case, as illustrated in FIG.23B, since the display element can emit light, the circuit 5365 and thelighting device 5366 can be eliminated. In addition, in order to supplyelectric power to the display element, a plurality of wirings 5373 whichcan serve as power supply lines can be provided in the pixel portion5364. The circuit 5361 can supply power supply voltage called voltage(ANO) to the wirings 5373. The wirings 5373 can be separately connectedto the pixels in accordance with color elements or connected to all thepixels.

Note that FIG. 23B illustrates an example in which the circuit 5361supplies different signals to the circuit 5363_1 and the circuit 5363_2.The circuit 5361 supplies a signal such as a scan line driver circuitstart signal (GSP1), a scan line driver circuit clock signal (GCK1), ora scan line driver circuit inverted clock signal (GCKB1) to the circuit5363_1. In addition, the circuit 5361 supplies a signal such as a scanline driver circuit start signal (GSP2), a scan line driver circuitclock signal (GCK2), or a scan line driver circuit inverted clock signal(GCKB2) to the circuit 5363_2. In this case, the circuit 5363_1 can scanonly wirings in odd-numbered rows of the plurality of wirings 5372 andthe circuit 5363_2 can scan only wirings in even-numbered rows of theplurality of wirings 5372. Thus, the driving frequency of the circuit5363_1 and the circuit 5363_2 can be lowered, so that power consumptioncan be reduced. Alternatively, an area in which a flip-flop of one stagecan be laid out can be made large. Therefore, a display device can havehigher definition. Alternatively, a display device can be made large.Note that this embodiment is not limited to this. As in FIG. 23A, thecircuit 5361 can supply the same signal to the circuit 5363_1 and thecircuit 5363_2.

Note that as in FIG. 23B, the circuit 5361 can supply different signalsto the circuit 5363_1 and the circuit 5363_2 in FIG. 23A.

Thus far, the example of a system block of a display device isdescribed.

Next, examples of structures of the display devices are described withreference to FIGS. 24A to 24E.

In FIG. 24A, circuits which have a function of outputting signals to thepixel portion 5364 (e.g., the circuit 5362, the circuit 5363_1, and thecircuit 5363_2) are formed over the same substrate 5380 as the pixelportion 5364. In addition, the circuit 5361 is formed over a differentsubstrate from the pixel portion 5364. In this manner, since the numberof external components is reduced, reduction in cost can be achieved.Alternatively, since the number of signals or voltages input to thesubstrate 5380 is reduced, the number of connections between thesubstrate 5380 and the external component can be reduced. Therefore,improvement in reliability or the increase in yield can be achieved.

Note that in the case where the circuit is formed over a differentsubstrate from the pixel portion 5364, the substrate can be mounted onan FPC (flexible printed circuit) by TAB (tape automated bonding).Alternatively, the substrate can be mounted on the same substrate 5380as the pixel portion 5364 by COG (chip on glass).

Note that in the case where the circuit is formed over a differentsubstrate from the pixel portion 5364, a transistor formed using asingle crystal semiconductor can be formed on the substrate. Therefore,the circuit formed over the substrate can have advantages such asimprovement in driving frequency, improvement in driving voltage, andsuppression of variations in output signals.

Note that a signal, voltage, current, or the like is input from anexternal circuit through an input terminal 5381 in many cases.

In FIG. 24B, circuits with low driving frequency (e.g., the circuit5363_1 and the circuit 5363_2) are formed over the same substrate 5380as the pixel portion 5364. In addition, the circuit 5361 and the circuit5362 are formed over a different substrate from the pixel portion 5364.In this manner, since the circuit formed over the substrate 5380 can beformed using a transistor with low mobility, a non-single-crystalsemiconductor, a microcrystalline semiconductor, an organicsemiconductor, an oxide semiconductor, or the like can be used for asemiconductor layer of the transistor. Accordingly, the increase in thesize of the display device, reduction in the number of steps, reductionin cost, improvement in yield, or the like can be achieved.

Note that as illustrated in FIG. 24C, part of the circuit 5362 (acircuit 5362 a) can be formed over the same substrate 5380 as the pixelportion 5364 and the other part of the circuit 5362 (a circuit 5362 b)can be formed over a different substrate from the pixel portion 5364.The circuit 5362 a includes a circuit which can be formed using atransistor with low mobility (e.g., a shift register, a selector, or aswitch) in many cases. In addition, the circuit 5362 b includes acircuit which is preferably formed using a transistor with high mobilityand few variations in characteristics (e.g., a shift register, a latchcircuit, a buffer circuit, a DA converter circuit, or an AD convertercircuit) in many cases. In this manner, as in FIG. 24B, anon-single-crystal semiconductor, a microcrystalline semiconductor, anorganic semiconductor, an oxide semiconductor, or the like can be usedfor a semiconductor layer of the transistor. Further, reduction inexternal components can be achieved.

In FIG. 24D, circuits which have a function of outputting signals to thepixel portion 5364 (e.g., the circuit 5362, the circuit 5363_1, and thecircuit 5363_2) and a circuit which has a function of controlling thesecircuits (e.g., the circuit 5361) are formed over a different substratefrom the pixel portion 5364. In this manner, since the pixel portion andperipheral circuits thereof can be formed over different substrates,improvement in yield can be achieved.

Note that as in FIG. 24D, the circuit 5363_1 and the circuit 5363_2 canbe formed over a different substrate from the pixel portion 5364 inFIGS. 24A to 24C.

In FIG. 24E, part of the circuit 5361 (a circuit 5361 a) is formed overthe same substrate 5380 as the pixel portion 5364 and the other part ofthe circuit 5361 (a circuit 5361 b) is formed over a different substratefrom the pixel portion 5364. The circuit 5361 a includes a circuit whichcan be formed using a transistor with low mobility (e.g., a switch, aselector, or a level shift circuit) in many cases. In addition, thecircuit 5361 b includes a circuit which is preferably formed using atransistor with high mobility and few variations (e.g., a shiftregister, a timing generator, an oscillator, a regulator, or an analogbuffer) in many cases.

Note that also in FIGS. 24A to 24D, the circuit 5361 a can be formedover the same substrate as the pixel portion 5364 and the circuit 5361 bcan be formed over a different substrate from the pixel portion 5364.

(Embodiment 11)

In this embodiment, examples of structures of transistors are describedwith reference to FIGS. 25A to 25C.

FIG. 25A illustrates an example of the structure of a top-gatetransistor and an example of a display element formed over thetransistor. FIG. 25B illustrates an example of the structure of abottom-gate transistor and an example of a display element formed overthe transistor.

The transistor in FIG. 25A includes a substrate 5260; an insulatinglayer 5261 formed over the substrate 5260; a semiconductor layer 5262which is formed over the insulating layer 5261 and is provided with aregion 5262 a, a region 5262 b, a region 5262 c, a region 5262 d, and aregion 5262 e; an insulating layer 5263 formed so as to cover thesemiconductor layer 5262; a conductive layer 5264 formed over thesemiconductor layer 5262 and the insulating layer 5263; an insulatinglayer 5265 which is formed over the insulating layer 5263 and theconductive layer 5264 and is provided with openings; and a conductivelayer 5266 which is formed over the insulating layer 5265 and in theopenings formed in the insulating layer 5265.

The transistor in FIG. 25B includes a substrate 5300; a conductive layer5301 formed over the substrate 5300; an insulating layer 5302 formed soas to cover the conductive layer 5301; a semiconductor layer 5303 aformed over the conductive layer 5301 and the insulating layer 5302; asemiconductor layer 5303 b formed over the semiconductor layer 5303 a; aconductive layer 5304 formed over the semiconductor layer 5303 b and theinsulating layer 5302; an insulating layer 5305 which is formed over theinsulating layer 5302 and the conductive layer 5304 and is provided withan opening; and a conductive layer 5306 which is formed over theinsulating layer 5305 and in the opening formed in the insulating layer5305.

The transistor in FIG. 25C includes a semiconductor substrate 5352including a region 5353 and a region 5355; an insulating layer 5356formed over the semiconductor substrate 5352; an insulating layer 5354formed over the semiconductor substrate 5352; a conductive layer 5357formed over the insulating layer 5356; an insulating layer 5358 which isformed over the insulating layer 5354, the insulating layer 5356, andthe conductive layer 5357 and is provided with openings; and aconductive layer 5359 which is formed over the insulating layer 5358 andin the openings formed in the insulating layer 5358. Thus, a transistoris formed in each of a region 5350 and a region 5351.

Note that in each of the structures of the transistors illustrated inFIGS. 25A to 25C as illustrated in FIG. 25A, over the transistor, it ispossible to form an insulating layer 5267 which is formed over theconductive layer 5266 and the insulating layer 5265 and is provided withan opening; a conductive layer 5268 which is formed over the insulatinglayer 5267 and in the opening formed in the insulating layer 5267; aninsulating layer 5269 which is formed over the insulating layer 5267 andthe conductive layer 5268 and is provided with an opening; alight-emitting layer 5270 which is formed over the insulating layer 5269and in the opening formed in the insulating layer 5269; and a conductivelayer 5271 formed over the insulating layer 5269 and the light-emittinglayer 5270.

Note that in each of the structures of the transistors illustrated inFIGS. 25A to 25C, as illustrated in FIG. 25A, over the transistor, it ispossible to form a liquid crystal layer 5307 which is formed over theinsulating layer 5305 and the conductive layer 5306 and a conductivelayer 5308 which is formed over the liquid crystal layer 5307.

The insulating layer 5261 can serve as a base film. The insulating layer5354 serves as an element isolation layer (e.g., a field oxide film).Each of the insulating layer 5263, the insulating layer 5302, and theinsulating layer 5356 can serve as a gate insulating film. Each of theconductive layer 5264, the conductive layer 5301, and the conductivelayer 5357 can serve as a gate electrode. Each of the insulating layer5265, the insulating layer 5267, the insulating layer 5305, and theinsulating layer 5358 can serve as an interlayer film or a planarizationfilm. Each of the conductive layer 5266, the conductive layer 5304, andthe conductive layer 5359 can serve as a wiring, an electrode of atransistor, an electrode of a capacitor, or the like. Each of theconductive layer 5268 and the conductive layer 5306 can serve as a pixelelectrode, a reflective electrode, or the like. The insulating layer5269 can serve as a partition wall. Each of the conductive layer 5271and the conductive layer 5308 can serve as a counter electrode, a commonelectrode, or the like.

As each of the substrate 5260 and the substrate 5300, a glass substrate,a quartz substrate, a semiconductor substrate (e.g., a silicon substrateor a single crystal substrate), an SOI substrate, a plastic substrate, ametal substrate, a stainless steel substrate, a substrate includingstainless steel foil, a tungsten substrate, a substrate includingtungsten foil, a flexible substrate, or the like can be used, forexample. As a glass substrate, a barium borosilicate glass substrate, analumino borosilicate glass substrate, or the like can be used, forexample. For a flexible substrate, a flexible synthetic resin such asplastics typified by polyethylene terephthalate (PET), polyethylenenaphthalate (PEN), or polyether sulfone (PES), or acrylic can be used,for example. Alternatively, an attachment film (formed usingpolypropylene, polyester, vinyl, polyvinyl fluoride, polyvinyl chloride,or the like), paper including a fibrous material, a base material film(formed using polyester, polyamide, polyimide, an inorganic vapordeposition film, paper, or the like), or the like can be used.

As the semiconductor substrate 5352, for example, a single crystalsilicon substrate having n-type or p-type conductivity can be used. Notethat this embodiment is not limited to this, parts or all the substratesthat can be used as the semiconductor substrate 5352 can be used as thesemiconductor substrate 5352. For example, the region 5353 is a regionwhere an impurity is added to the semiconductor substrate 5352 andserves as a well. For example, in the case where the semiconductorsubstrate 5352 has p-type conductivity, the region 5353 has n-typeconductivity and serves as an n-well. On the other hand, in the casewhere the semiconductor substrate 5352 has n-type conductivity, theregion 5353 has p-type conductivity and serves as a p-well. For example,the region 5355 is a region where an impurity is added to thesemiconductor substrate 5352 and serves as a source region or a drainregion. Note that an LDD region can be formed in the semiconductorsubstrate 5352.

For the insulating layer 5261, a single-layer structure or a layeredstructure of an insulating film containing oxygen or nitrogen, such assilicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride(SiO_(x)N_(y)) (x>y>0), or silicon nitride oxide (SiN_(x)O_(y)) (x>y>0)can be used, for example. In an example in the case where the insulatinglayer 5261 has a two-layer structure, a silicon nitride film and asilicon oxide film can be formed as a first insulating layer and asecond insulating layer, respectively. In an example in the case wherethe insulating layer 5261 has a three-layer structure, a silicon oxidefilm, a silicon nitride film, and a silicon oxide film can be formed asa first insulating layer, a second insulating layer, and a thirdinsulating layer, respectively.

For each of the semiconductor layer 5262, the semiconductor layer 5303a, and the semiconductor layer 5303 b, for example, a non-single-crystalsemiconductor (e.g., amorphous silicon, polycrystalline silicon, ormicrocrystalline silicon), a single crystal semiconductor, a compoundsemiconductor or an oxide semiconductor (e.g., ZnO, InGaZnO, SiGe, GaAs,IZO (indium zinc oxide), ITO (indium tin oxide), SnO, TiO, or AlZnSnO(AZTO)), an organic semiconductor, a carbon nanotube, or the like can beused.

Note that for example, the region 5262 a is an intrinsic region where animpurity is not added to the semiconductor layer 5262 and serves as achannel region. However, an impurity can be added to the region 5262 a.The concentration of the impurity added to the region 5262 a ispreferably lower than the concentration of an impurity added to theregion 5262 b, the region 5262 c, the region 5262 d, or the region 5262e. Each of the region 5262 b and the region 5262 d is a region to whichan impurity is added at lower concentration as compared to the region5262 c or the region 5262 e and serves as an LDD (lightly doped drain)region. Note that the region 5262 b and the region 5262 d can beeliminated. Each of the region 5262 c and the region 5262 e is a regionto which an impurity is added at high concentration and serves as asource region or a drain region.

Note that the semiconductor layer 5303 b is a semiconductor layer towhich phosphorus or the like is added as an impurity element and hasn-type conductivity.

Note that in the case where an oxide semiconductor or a compoundsemiconductor is used for the semiconductor layer 5303 a, thesemiconductor layer 5303 b can be eliminated.

For each of the insulating layer 5263, the insulating layer 5302, andthe insulating layer 5356, a single-layer structure or a layeredstructure of an insulating film containing oxygen or nitrogen, such assilicon oxide (SiO_(x)), silicon nitride (SiN_(x)), silicon oxynitride(SiO_(x)N_(y)) (x>y>0), or silicon nitride oxide (SiN_(x)O_(y)) (x>y>0)can be used, for example.

As each of the conductive layer 5264, the conductive layer 5266, theconductive layer 5268, the conductive layer 5271, the conductive layer5301, the conductive layer 5304, the conductive layer 5306, theconductive layer 5308, the conductive layer 5357, and the conductivelayer 5359, for example, a conductive film having a single-layerstructure or a layered structure, or the like can be used. For example,for the conductive film, the group consisting of aluminum (Al), tantalum(Ta), titanium (Ti), molybdenum (Mo), tungsten (W), neodymium (Nd),chromium (Cr), nickel (Ni), platinum (Pt), gold (Au), silver (Ag),copper (Cu), manganese (Mn), cobalt (Co), niobium (Nb), silicon (Si),iron (Fe), palladium (Pd), carbon (C), scandium (Sc), zinc (Zn), gallium(Ga), indium (In), tin (Sn), zirconium (Zr), and cerium (Ce); asingle-layer film containing one element selected from the above group;a compound containing one or more elements selected from the abovegroup; or the like can be used. Note that the single-layer film or thecompound can contain phosphorus (P), boron (B), arsenic (As), and/oroxygen (O), for example. Alternatively, for example, a film including ahigh molecular film, a film including conductive plastics (e.g.,polyethylene dioxythiophene (PEDOT)), or the like can be used as theconductive film.

For example, a compound containing one or more elements selected fromthe above plurality of elements (e.g., an alloy), a compound containingnitrogen and one or more elements selected from the above plurality ofelements (e.g., a nitride film), a compound containing silicon and oneor more elements selected from the above plurality of elements (e.g., asilicide film), a nanotube material, or the like can be used as thecompound. For example, indium tin oxide (ITO), indium zinc oxide (IZO),indium tin oxide containing silicon oxide (ITSO), zinc oxide (ZnO), tinoxide (SnO), cadmium tin oxide (CTO), aluminum-neodymium (Al—Nd),aluminum-tungsten (Al—W), aluminum-zirconium (Al—Zr), aluminum titanium(Al—Ti), aluminum-cerium (Al—Ce), magnesium-silver (Mg—Ag),molybdenum-niobium (Mo—Nb), molybdenum-tungsten (Mo—W),molybdenum-tantalum (Mo—Ta), or the like can be used as an alloy. Forexample, titanium nitride, tantalum nitride, molybdenum nitride, or thelike can be used for a nitride film. For example, tungsten silicide,titanium silicide, nickel silicide, aluminum silicon, molybdenumsilicon, or the like can be used for a silicide film. For example, acarbon nanotube, an organic nanotube, an inorganic nanotube, a metalnanotube, or the like can be used as a nanotube material.

Note that silicon (Si) can contain an n-type impurity (e.g., phosphorus)or a p-type impurity (e.g., boron). When silicon contains the impurity,conductivity can be increased or a function which is similar to that ofa normal conductor can be realized. Thus, it can be utilized easily as awiring, an electrode, or the like.

Note that as silicon, silicon with various levels of crystallinity, suchas single crystal silicon, polycrystalline silicon (polysilicon), ormicrocrystalline (microcrystal) silicon; or silicon withoutcrystallinity, such as amorphous silicon; or the like can be used. Byusing single crystal silicon or polycrystalline silicon as silicon, theresistance of a wiring, an electrode, a conductive layer, a conductivefilm, a terminal, or the like can be reduced. By using amorphous siliconor microcrystalline silicon as silicon, a wiring or the like can beformed through a simple process.

Note that in the case where a semiconductor material such as silicon isused for the conductive layer, the semiconductor material such assilicon can be formed at the same time as a semiconductor layer of atransistor.

Aluminum and silver have high conductivity, so that signal delay can bereduced. Further, since aluminum and silver can be easily etched, theyare easily patterned and can be minutely processed.

Note that since copper has high conductivity, signal delay can bereduced. In the case where copper is used for the conductive layer, alayered structure is preferably used in order to improve adhesion.

Note that molybdenum and titanium are preferable because even ifmolybdenum and titanium are in contact with an oxide semiconductor(e.g., ITO or IZO) or silicon, molybdenum and titanium do not causedefects easily. Further, molybdenum and titanium are preferable becausemolybdenum and titanium are easily etched and have high heat resistance.Thus, molybdenum or titanium is preferably used for a conductive layerwhich is in contact with an oxide semiconductor or silicon.

Note that tungsten is preferable because it has advantages such as highheat resistance.

Note that neodymium is preferable because it has advantages such as highheat resistance. In particular, when an alloy material of neodymium andaluminum is used for the conductive layer, aluminum does not causehillocks easily. Note that this embodiment is not limited to this, andaluminum does not cause hillocks easily when an alloy material ofaluminum and tantalum, zirconium, titanium, or cerium is used. Inparticular, an alloy material of aluminum and cerium can reduce arcingdrastically.

Note that since ITO, IZO, ITSO, ZnO, Si, SnO, CTO, a carbon nanotube, orthe like has light-transmitting properties, such a material can be usedfor a portion through which light passes, such as a pixel electrode, acounter electrode, or a common electrode. In particular, IZO ispreferable because it is easily etched and processed. In etching IZO,residues are hardly left. Therefore, when IZO is used for a pixelelectrode, defects (e.g., short circuit or orientation disorder) of aliquid crystal element or a light-emitting element can be reduced.

Note that the conductive layer can have either a single-layer structureor a multi-layer structure. When a single-layer structure is employed, amanufacturing process of a wiring, an electrode, a conductive layer, aconductive film, a terminal, or the like can be simplified, the numberof days for a process can be reduced, and cost can be reduced. On theother hand, when a multi-layer structure is employed, a wiring, anelectrode, or the like with high quality can be formed while anadvantage of each material is utilized and a disadvantage thereof isreduced. For example, when a low-resistant material (e.g., aluminum) isincluded in a multi-layer structure, the resistance of a wiring can bereduced. As another example, with a layered structure in which a lowheat-resistant material is interposed between high heat-resistantmaterials, the heat resistance of a wiring, an electrode, or the likecan be increased while utilizing an advantage of the low heat-resistantmaterial. As an example of such a layered structure, it is preferable toemploy a layered structure in which a layer containing aluminum isinterposed between layers containing molybdenum, titanium, neodymium, orthe like.

Note that when wirings, electrodes, or the like are in direct contactwith each other, they adversely affect each other in some cases. Forexample, one wiring or one electrode is mixed into a material of anotherwiring or another electrode and changes its properties, whereby anintended function cannot be obtained in some cases. As another example,when a high-resistant portion is formed, a problem may occur so that theportion cannot be formed normally. In such cases, a material whoseproperties are changed by reaction with a different material can beinterposed between or covered with materials which do not easily reactwith the different material. For example, in the case where ITO andaluminum are connected to each other, titanium, molybdenum, or an alloyof neodymium can be interposed between ITO and aluminum. For example, inthe case where silicon and aluminum are connected to each other,titanium, molybdenum, or an alloy of neodymium can be interposed betweensilicon and aluminum.

Note that such a material can be used for a wiring, an electrode, aconductive layer, a conductive film, a terminal, a via, a plug, or thelike.

For each of the insulating layer 5265, the insulating layer 5267, theinsulating layer 5269, the insulating layer 5305, and the insulatinglayer 5358, an insulating layer having a single-layer structure or alayered structure, or the like can be used, for example. For example, asthe insulating layer, an insulating film containing oxygen or nitrogen,such as silicon oxide (SiO_(x)), silicon nitride (SiN_(x)), siliconoxynitride (SiO_(x)N_(y)) (x>y>0), or silicon nitride oxide(SiN_(x)O_(y)) (x>y>0); a film containing carbon such as diamond-likecarbon (DLC); an organic material such as a siloxane resin, epoxy,polyimide, polyamide, polyvinyl phenol, benzocyclobutene, or acrylic; orthe like can be used.

For the light-emitting layer 5270, an organic EL element, an inorganicEL element, or the like can be used, for example. For the organic ELelement, for example, a single-layer structure or a layered structure ofa hole injection layer formed using a hole injection material, a holetransport layer formed using a hole transport material, a light-emittinglayer formed using a light-emitting material, an electron transportlayer formed using an electron transport material, an electron injectionlayer formed using an electron injection material, or a layer in which aplurality of these materials are mixed can be used.

For example, the following can be used for the liquid crystal layer5307, a liquid crystal material which can be used for the liquid crystallayer 5307, or a liquid crystal mode which can be used for a liquidcrystal element including the liquid crystal layer 5307: a nematicliquid crystal, a cholesteric liquid crystal, a smectic liquid crystal,a discotic liquid crystal, a thermotropic liquid crystal, a lyotropicliquid crystal, a low-molecular liquid crystal, a high-molecular liquidcrystal, a polymer dispersed liquid crystal (PDLC), a ferroelectricliquid crystal, an anti-ferroelectric liquid crystal, a main-chainliquid crystal, a side-chain high-molecular liquid crystal, a plasmaaddressed liquid crystal (PALC), a banana-shaped liquid crystal, a TN(twisted nematic) mode, an STN (super twisted nematic) mode, an IPS(in-plane-switching) mode, an FFS (fringe field switching) mode, an MVA(multi-domain vertical alignment) mode, a PVA (patterned verticalalignment) mode, an ASV (advanced super view) mode, an ASM (axiallysymmetric aligned microcell) mode, an OCB (optically compensatedbirefringence) mode, an ECB (electrically controlled birefringence)mode, an FLC (ferroelectric liquid crystal) mode, an AFLC(anti-ferroelectric liquid crystal) mode, a PDLC (polymer dispersedliquid crystal) mode, a guest-host mode, a blue phase mode, and thelike.

Note that an insulating layer which serves as an alignment film, aninsulating layer which serves as a protrusion portion, or the like canbe formed over the insulating layer 5305 and the conductive layer 5306.

Note that an insulating layer or the like which serves as a colorfilter, a black matrix, or a protrusion portion can be formed over theconductive layer 5308. An insulating layer which serves as an alignmentfilm can be formed below the conductive layer 5308.

Note that the insulating layer 5269, the light-emitting layer 5270, andthe conductive layer 5271 can be eliminated in the cross-sectionalstructure in FIG. 25A, and the liquid crystal layer 5307 and theconductive layer 5308 which are illustrated in FIG. 25B can be formedover the insulating layer 5267 and the conductive layer 5268.

Note that the liquid crystal layer 5307 and the conductive layer 5308can be eliminated in the cross-sectional structure in FIG. 25B, and theinsulating layer 5269, the light-emitting layer 5270, and the conductivelayer 5271 which are illustrated in FIG. 25A can be formed over theinsulating layer 5305 and the conductive layer 5306.

Note that in the cross-sectional structure in FIG. 25C, the insulatinglayer 5269, the light-emitting layer 5270, and the conductive layer 5271which are illustrated in FIG. 25A can be formed over the insulatinglayer 5358 and the conductive layer 5359. Alternatively, the liquidcrystal layer 5307 and the conductive layer 5308 which are illustratedin FIG. 25B can be formed over the insulating layer 5267 and theconductive layer 5268.

(Embodiment 12)

In this embodiment, examples of electronic devices are described.

FIGS. 26A to 26H and FIGS. 27A to 27D illustrate electronic devices.These electronic devices can include a housing 5000, a display portion5001, a speaker 5003, an LED lamp 5004, operation keys 5005 (including apower switch or an operation switch), a connection terminal 5006, asensor 5007 (a sensor having a function of measuring force,displacement, position, speed, acceleration, angular velocity,rotational frequency, distance, light, liquid, magnetism, temperature,chemical substance, sound, time, hardness, electric field, current,voltage, electric power, radiation, flow rate, humidity, gradient,oscillation, odor, or infrared ray), a microphone 5008, and the like.

FIG. 26A illustrates a mobile computer, which can include a switch 5009,an infrared port 5010, and the like in addition to the above objects.FIG. 26B illustrates a portable image regenerating device provided witha memory medium (e.g., a DVD regenerating device), which can include asecond display portion 5002, a memory medium reading portion 5011, andthe like in addition to the above objects. FIG. 26C illustrates agoggle-type display, which can include the second display portion 5002,a support portion 5012, an earphone 5013, and the like in addition tothe above objects. FIG. 26D illustrates a portable game machine, whichcan include the memory medium reading portion 5011 and the like inaddition to the above objects. FIG. 26E illustrates a projector, whichcan include a light source 5033, a projector lens 5034, and the like inaddition to the above objects. FIG. 26F illustrates a portable gamemachine, which can include the second display portion 5002, the memorymedium reading portion 5011, and the like in addition to the aboveobjects. FIG. 26G illustrates a television receiver, which can include atuner, an image processing portion, and the like in addition to theabove objects. FIG. 26H illustrates a portable television receiver,which can include a charger 5017 capable of transmitting and receivingsignals and the like in addition to the above objects. FIG. 27Aillustrates a display, which can include a support base 5018 and thelike in addition to the above objects. FIG. 27B illustrates a camera,which can include an external connecting port 5019, a shutter button5015, an image receiving portion 5016, and the like in addition to theabove objects. FIG. 27C illustrates a computer, which can include apointing device 5020, the external connecting port 5019, a reader/writer5021, and the like in addition to the above objects. FIG. 27Dillustrates a mobile phone, which can include an antenna 5014, a tunerof one-segment (1 seg digital TV broadcasts) partial reception servicefor mobile phones and mobile terminals, and the like in addition to theabove objects.

The electronic devices illustrated in FIGS. 26A to 26H and FIGS. 27A to27D can have a variety of functions, for example, a function ofdisplaying a lot of information (e.g., a still image, a moving image,and a text image) on a display portion; a touch panel function; afunction of displaying a calendar, date, time, and the like; a functionof controlling processing with a lot of software (programs); a wirelesscommunication function; a function of being connected to a variety ofcomputer networks with a wireless communication function; a function oftransmitting and receiving a lot of data with a wireless communicationfunction; and a function of reading a program or data stored in a memorymedium and displaying the program or data on a display portion. Further,the electronic device including a plurality of display portions can havea function of displaying image information mainly on one display portionwhile displaying text information on another display portion, a functionof displaying a three-dimensional image by displaying images whereparallax is considered on a plurality of display portions, or the like.Furthermore, the electronic device including an image receiving portioncan have a function of photographing a still image, a function ofphotographing a moving image, a function of automatically or manuallycorrecting a photographed image, a function of storing a photographedimage in a memory medium (an external memory medium or a memory mediumincorporated in the camera), a function of displaying a photographedimage on the display portion, or the like. Note that functions which canbe provided for the electronic devices illustrated in FIGS. 26A to 26Hand FIGS. 27A to 27D are not limited them, and the electronic devicescan have a variety of functions.

The electronic devices described in this embodiment each include adisplay portion for displaying some kind of information.

Next, applications of semiconductor devices are described.

FIG. 27E illustrates an example in which a semiconductor device isincorporated in a building structure. FIG. 27E illustrates a housing5022, a display portion 5023, a remote controller 5024 which is anoperation portion, a speaker 5025, and the like. The semiconductordevice is incorporated in the building structure as a wall-hanging typeand can be provided without requiring a large space.

FIG. 27F illustrates another example in which a semiconductor device isincorporated in a building structure. A display panel 5026 isincorporated in a prefabricated bath unit 5027, so that a bather canview the display panel 5026.

Note that although this embodiment describes the wall and theprefabricated bath are given as examples of the building structures,this embodiment is not limited to them. The semiconductor devices can beprovided in a variety of building structures.

Next, examples in which semiconductor devices are incorporated in movingobjects are described.

FIG. 27G illustrates an example in which a semiconductor device isincorporated in a car. A display panel 5028 is incorporated in a carbody 5029 of the car and can display information related to theoperation of the car or information input from inside or outside of thecar on demand. Note that the display panel 5028 may have a navigationfunction.

FIG. 27H illustrates an example in which a semiconductor device isincorporated in a passenger airplane. FIG. 27H illustrates a usagepattern when a display panel 5031 is provided for a ceiling 5030 above aseat of the passenger airplane. The display panel 5031 is incorporatedin the ceiling 5030 through a hinge portion 5032, and a passenger canview the display panel 5031 by stretching of the hinge portion 5032. Thedisplay panel 5031 has a function of displaying information by theoperation of the passenger.

Note that although bodies of a car and an airplane are illustrated asexamples of moving objects in this embodiment, this embodiment is notlimited to them. The semiconductor devices can be provided for a varietyof objects such as two-wheeled vehicles, four-wheeled vehicles(including cars, buses, and the like), trains (including monorails,railroads, and the like), and vessels.

This application is based on Japanese Patent Application serial no.2009-094306 filed with Japan Patent Office on Apr. 8, 2009, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. A display device comprising: a pixel portion; anda backlight under the pixel portion, the backlight comprising a firstlight source, a second light source, and a light guiding plate, wherein,depending on image signals supplied to the pixel portion, luminance ofthe first light source is different from luminance of the second lightsource, wherein the first light source is provided adjacent to a firstend of the light guiding plate, wherein the second light source isprovided adjacent to a second end facing the first end of the lightguiding plate, wherein each of the first light source and the secondlight source comprises a white light emitting element and light emittingelements of at least three colors other than white, and wherein each ofthe first light source and the second light source is configured to emitwhite light using only the white light emitting element.
 2. The displaydevice according to claim 1, wherein the luminance of the first lightsource and the second light source is independently controllable.
 3. Thedisplay device according to claim 1, further comprising a diffusingplate between the backlight and the pixel portion.
 4. The display deviceaccording to claim 1, wherein the white light emitting element comprisesa white light emitting diode.
 5. The display device according to claim1, wherein the light emitting elements of at least three colors otherthan white comprise a red light emitting diode, a blue light emittingdiode, and a green light emitting diode.
 6. A display device comprising:a pixel portion; and a backlight under the pixel portion, the backlightcomprising a first light emitting element, a second light emittingelement, and a light guiding plate, wherein, depending on image signalssupplied to the pixel portion, luminance of the first light emittingelement is different from luminance of the second light emittingelement, wherein the first light emitting element is provided adjacentto a first end of the light guiding plate, wherein the second lightemitting element is provided adjacent to a second end facing the firstend of the light guiding plate, wherein each of the first light emittingelement and the second light emitting element comprises a white lightemitting diode and light emitting diodes of at least three colors otherthan white, and wherein each of the first light emitting element and thesecond light emitting element is configured to emit white light usingonly the white light emitting diode.
 7. The display device according toclaim 6, wherein the luminance of the first light emitting element andthe second light emitting element is independently controllable.
 8. Thedisplay device according to claim 6, further comprising a diffusingplate between the backlight and the pixel portion.
 9. The display deviceaccording to claim 6, wherein the light emitting diodes of at leastthree colors other than white comprise a red light emitting diode, ablue light emitting diode, and a green light emitting diode.
 10. Adisplay device comprising: a pixel portion; and a backlight under thepixel portion, the backlight comprising a plurality of first lightsources, a plurality of second light sources, and a light guiding plate,wherein, depending on image signals supplied to the pixel portion,luminance of the plurality of first light sources is different fromluminance of the plurality of second light sources, wherein theplurality of first light sources are provided adjacent to a first end ofthe light guiding plate, wherein the plurality of second light sourcesare provided adjacent to a second end facing the first end of the lightguiding plate, wherein each of the plurality of first light sources andthe plurality of second light sources comprises a white light emittingelement and light emitting elements of at least three colors other thanwhite, and wherein each of the plurality of first light sources and theplurality of second light sources is configured to emit white light. 11.The display device according to claim 10, wherein the luminance of theplurality of first light sources and the plurality of second lightsources is independently controllable.
 12. The display device accordingto claim 10, further comprising a diffusing plate between the backlightand the pixel portion.
 13. The display device according to claim 10,wherein the white light emitting element comprises a white lightemitting diode.
 14. The display device according to claim 10, whereinthe light emitting elements of at least three colors other than whitecomprise a red light emitting diode, a blue light emitting diode, and agreen light emitting diode.